The effect of film growth rate on the structure and intrinsic stresses of thin (100 nm) Ge films grown on GaAs(100) substrates was investigate by High Resolution X-Ray Diffraction (HRXRD). The Ge films were deposited onto GaAs using thermal evaporation of Ge in the vacuum. It was shown that pseudomor-phic films with good structural quality can be obtained by this growth technique. We found out that the films have biaxial deformations due to coherent interface and Poisson ratio. The films are elastically com-pressed in the interface and stretched in the perpendicular [001] direction. The intrinsic deformations of thin Ge films strongly depended on the deposition rate. Their correlations with surface roughness, electri-cal and optical parameters are discussed.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3531

Kholevchuk, V.V.

Kladko, V.P.

Kuchuk, A.V.

Lytvyn, P.M.

Matveeva, L.A.

Mitin, V.F.

SocioEconomic Challenges Journal (Sumy State University)

PROCEEDINGS OF THE INTERNATIONAL CONFERENCE  
NANOMATERIALS: APPLICATIONS AND PROPERTIES 
Vol. 2 No 1, 01PCSI20(4pp) (2013) 
 
 
2304-1862/2013/2(1)01PCSI20(4) 01PCSI20-1  2013 Sumy State University 
Study of Structure and Intrinsic Stresses of Ge Thin Films on GaAs 
 
V.V. Kholevchuk, V.P. Kladko, A.V. Kuchuk, P.M. Lytvyn, L.A. Matveeva, V.F. Mitin* 
 
V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine, 03028 Kyiv, Ukraine 
 
(Received 13 June 2013; published online 01 September 2013) 
 
The effect of film growth rate on the structure and intrinsic stresses of thin ( 100 nm) Ge films grown 
on GaAs(100) substrates was investigate by High Resolution X-Ray Diffraction (HRXRD). The Ge films 
were deposited onto GaAs using thermal evaporation of Ge in the vacuum. It was shown that pseudomor-
phic films with good structural quality can be obtained by this growth technique. We found out that the 
films have biaxial deformations due to coherent interface and Poisson ratio. The films are elastically com-
pressed in the interface and stretched in the perpendicular [001] direction. The intrinsic deformations of 
thin Ge films strongly depended on the deposition rate. Their correlations with surface roughness, electri-
cal and optical parameters are discussed. 
 
Keywords: Ge/GaAs, High resolution X-ray diffraction, Intrinsic stresses 
 
 PACS numbers: 61.05.cp, 68.55.− a 
 
 
                                                          
* mitin@isp.kiev.ua; mitin@microsensor.com.ua  
1. INTRODUCTION 
 
The Ge/GaAs heterostructure is promising for a 
number of practical applications such as high-
performance solar cells [1-4], metal oxide semiconduc-
tor field-effect transistors [5, 6], microwave diodes [7], 
and sensors, e.g. thermometers [8, 9], and -ray and op-
tical radiation detectors [8, 10-13]. In addition the 
Ge/GaAs is an excellent model system for IV/III-V het-
erostructures in general. This heterostructure is char-
acterized by close values of the components lattice con-
stants as well as practical coincidence of their thermal 
expansion coefficients [1]. These properties are favora-
ble for epitaxial growth and fabrication of films and 
heterojunctions with almost perfect structure. 
The defect formation in the Ge/GaAs heterostruc-
tures depends on which material serves as the sub-
strate (Ge or GaAs). In this work, we consider Ge film 
epitaxy on the GaAs(100) substrate. 
The Ge lattice constant exceeds that of GaAs. 
Therefore, the Ge films grown on GaAs substrates are 
compressed. It was experimentally shown [14] that 
elastically compressed Ge films on GaAs may exist up 
to film thickness of 5 m. In that case, there are no 
mismatch dislocations which could impair the electrical 
properties of the heterojunction. Thus, it is possible to 
form a high-quality interface (without misfit disloca-
tions) in the Ge/GaAs heterostructure. 
The distinguishing feature of Ge films on GaAs is 
the strong dependence of their structural, electrical 
and optical properties, on the method of preparation. 
This is related to possible interdiffusion of the joining 
materials [15-23]. For Ge films, diffused Ga and As at-
oms act as shallow acceptors and donors, respectively. 
Therefore, because of autodoping, the Ge films on GaAs 
may be p- or n-type with different degrees of compensa-
tion including fully compensated [8, 24-27]. Moreover 
the degree of structural perfection of the Ge films, as 
well as the concentration of structural defects in them, is 
determined by the film preparation condition. The Ge 
films can be amorphous, poly- or single crystalline, with 
different degrees of structural perfection. 
The pioneer work on fabrication and investigation 
of the Ge/GaAs heterostructure can be traced to the 
paper by Anderson [28]. A rather large number of stud-
ies has been done to understand the effect of factors 
such as: preparation methods, substrate temperature, 
film thickness and GaAs surface preparation on the 
growth mechanism [29-37], surface and heterobounda-
ry morphology [15, 23, 36-43], intrinsic stresses 
[12, 33, 39-42], electrical [15, 23, 28, 40, 46-48] and 
optical [23, 28, 46, 49] properties of Ge films on GaAs. 
However, the effect of the deposition rate on the prop-
erties of Ge films on GaAs remains not fully explored, 
with few studies considering only high deposition rates 
[50, 51]. 
In our previous [8, 24] and recent work [26, 27, 52] 
we show that deposition rate drastically affects the 
electrical and optical properties as well as surface mor-
phology of thin ( 100 nm) Ge films on GaAs. In particu-
lar we show that efficient control of the film properties 
can be achieved by varying their deposition rate. 
The subject of this paper is further in-depth study 
the effect of film growth rate with focus on structure 
and intrinsic stresses of thin Ge films by using High 
Resolution X-Ray Diffraction (HRXRD). Measured 
rocking curves show that pseudomorphic samples with 
good structural quality can be obtained by this growth 
technique. It was also shown that the films are elas-
tically compressed and intrinsic stresses strongly de-
pended on the deposition rate.  
 
2. PREPARATION CONDITIONS AND  
MEASUREMENT PROCEDURE 
 
The Ge films were deposited using thermal evapo-
ration of Ge in the vacuum (2×10-4 Pa) onto semi-
insulating (107 cm) GaAs(100) substrates. The tem-
perature of GaAs substrate during the film deposition 
was maintained at 500 C. The film deposition rate was 
maintained constant over the course of each deposition; 
and varied (0.02 0.35) nm/s for different specimens. 
The evaporation source was a glass-graphite crucible 
 V.V. KHOLEVCHUK, V.P. KLADKO, A.V. KUCHUK, ET. AL PROC. NAP 2, 01PCSI20 (2013) 
 
 
01PCSI20-2 
heated with electric current flowing through it. The 
deposition rate was set by the crucible current that 
determined the Ge evaporation temperature. The film 
thicknesses were 100±20 nm. Before Ge film deposi-
tion, the GaAs substrates were treated with the 
H2SO4:H2O2:H2O = 4:1:1 etchant for 3 min. and ther-
mal annealed in vacuum at 500 С for 15 min. 
The structural quality of Ge/GaAs heterostructure 
was studied by HRXRD using a Philips MRD diffrac-
tometer with a Cu anode X-ray beam. The X-ray source 
was operated at 40 kV and 40 mA. A four-crystal Bar-
tels monochromator was employed using four Ge 022 
reflections to provide a monochromatic beam with a 
divergence of 12 arcsec.  
The intrinsic stresses (σ) due to lattice mismatch 
between Ge and GaAs also were determined from the 
radius of curvature of specimen surfaces using a profil-
ograph and by application of the Stoney’s formula 
[53, 54], 2 [6(1 ) ]Et Rd  where E, t and ν are 
Young’s modulus, thickness and Poisson ratio of the 
substrate, respectively, d is the film thickness and R is 
the heterosystem bending radius. 
 
3. EXPERIMENTAL RESULTS AND DISCUS-
SION 
 
3.1 Structure and Intrinsic Stresses 
 
Fig. 1 shows the experimental and simulated rock-
ing curves (004 reflection) for Ge/GaAs films obtained 
at different growth rates. One can clearly observe the 
Bragg peaks for Ge and GaAs substrate. The Ge films 
are pseudomorphic. The in-plane Ge lattice constant is 
very close to that of GaAs, with corresponding lattice 
constant increasing in the perpendicular direction. The 
left-side shift of Ge film maximum in comparison with 
a bulk Ge single crystal is observed (Fig. 1). The verti-
cal dotted lines in Fig. 1 indicate the diffraction angle 
position for bulk Ge. 
At low deposition rate, the absence of interference 
fringes and higher intensity of tails are caused by some 
structural inhomogeneities of the film and interface 
roughness that were not taken into account at simula-
tions. 
At high growth rate, the interference fringes in the 
Ge film are observed (Fig. 1(b)), thus indicating phase 
coherency of the diffracted waves and high crystalline 
quality of this heterostructure. 
 The investigations of radius of curvature of the 
Ge/GaAs heterostructure showed that Ge films are 
compressed. The intrinsic stresses in the Ge films 
about 100 nm thick also calculated using the Stoney’s 
formula are at the level of several tenth parts of GPa. 
They depend on the film growth rate, decreasing from 
6.7 108 Pa to 2 108 Pa (i.e. by more than three times) 
as the deposition rate decreased from 0.35 nm/s to 
0.02 nm/s (Fig. 2). 
 
3.2 Surface Roughness, Electrical and Optical 
Parameters 
 
In our recent work [27, 52] we show that deposition 
rate also strongly affects the surface morphology, elec-
trical and optical properties of the Ge films. 
 
 
 
Fig. 1 – Rocking curves (004) for Ge films on GaAs. The film 
thickness was 100±20 nm. Ge growth deposition rates used are 
0.02 nm/s (a) and 0.35 nm/s (b). Vertical dotted line denotes 
position of diffraction maximum from the bulk Ge. Simulated 
dotted curves correspond to ideally pseudomorphic film. The 
blue curve in (b) is simulation fitted to experimental data  
 
 
 
Fig. 2 – Dependence of intrinsic stresses ( ) in Ge films on 
GaAs on the film growth rate (V). The film thickness was con-
stant (about 130 nm) 
 
The films prepared at high deposition rate have 
smooth surfaces with root-mean-square (RMS) rough-
ness of about 0.5 nm. In contrast, at low growth rate 
film roughness is large and can reach up to 14.6 nm in 
the film of 100 nm thick. 
 STUDY OF STRUCTURE AND INTRINSIC STRESSES … PROC. NAP 2, 01PCSI20 (2013) 
 
 
01PCSI20-3 
Optical absorption measurements of the Ge films 
show that at energies E < Eg, the optical absorption 
coefficient D depends on the photon energy E as 
]/)(exp[ EED g , where   dE/dlnD  is the charac-
teristic energy that determines the spreading of the 
fundamental absorption edge. For the Ge films in this 
study  does not depend on temperature. This exponen-
tial dependence D(E) is related to the tails in the densi-
ty-of-states in the Ge band gap. The existence of these 
tails permits optical transitions at photon energies be-
low Eg. Table 1 presents the  values for films obtained 
at different deposition rates. As the deposition rate 
decreased, the tails in the density of states, and there-
by the  value, increased. The degree of spreading of 
the fundamental absorption edge  can be varied from 
60 meV up to 140 meV. 
 
Table 1 – Dependencies of intrinsic stresses ( ), characteristic 
energy , resistivity ( ), activation energy of conductivity (ε1), 
conductivity type and root-mean-square (RMS) roughness for 
the Ge films of 100±20 nm thicknesses grown at different dep-
osition rates V. 
 
V (nm/s) 0.02 0.35 
 (Pa) 2 108 6.7 108 
RMS (nm) 14.6 0.49 
 ( /cm) 120 0.02 
1
 (eV) 0.35 0 
Conductivity type p n 
 (meV) 140 70 
The transport phenomena in Ge films obtained at 
low and high deposition rate also differ drastically. The 
Ge films obtained at high deposition rate are n-type, 
low-resistant (0.1-0.01 cm), heavily doped and slight-
ly compensated (Table 1). Temperature dependence of 
conductivity in these films is weak or practically ab-
sent. The films obtained at low deposition rate are p-
type, high-resistant ( 100 cm), heavily doped, and 
strongly compensated; in the limiting case fully com-
pensated. Their conductivity is thermally activated. 
The activation energy of conductivity can reach up to 
half of the Ge band gap (Table 1). 
 
4. CONCLUSION 
 
We present a HRXRD study of Ge/GaAs thin films. 
The measured rocking curves show that an ideally 
pseudomorphic growth of Ge films with good single 
crystal structure can be obtained by this growth tech-
nique. The film-substrate interface is coherent and dis-
location free. It was also shown that the films are elas-
tically compressed and intrinsic stresses strongly de-
pend on the deposition rate. This effect is essential and 
should be taken into account when developing and pro-
ducing devices based on the Ge/GaAs heterostructure. 
 
AKNOWLEDGEMENTS 
 
This work was partially funded under the Ukraini-
an State Program “Nanotechnologies and nanomateri-
als”, Projects No. 2.2.6.15 and 3.6.1.10. 
 
  
 
REFERENCES 
 
1. G. Milnes and D. L. Feucht, Heterojunctions and Metal-
Semiconductor Junctions (Academic, New York, 1972). 
2. M. Meyer, and R. A. Metzger, Compnd. Semicond. 2, 22 
(1996). 
3. C. Flores, B. Bollani, R. Campensato, D. Passoni, and 
G. L. Timò, Microelectron. Eng. 18, 175 (1992). 
4. S. J. Wojtczuk, S. P. Tobin, C. J. Keavney, C. Bajgar, 
M. M. Sanfacon, L. M. Geoffroy, T. M. Dixon, 
S. M. Vernon, J. D. Scofield, and D. S. Ruby, IEEE T. Elec-
tron. Dev. 37, 455 (1990). 
5. G.-L. Luo, Z.-Y. Han, C.-H. Chien, C.-H. Ko, C. H. Wann, H.-
Y. Lin, Y.-L. Shen, C.-T. Chung, S.-C. Huang, C.-C. Cheng, 
and C.-Y. Chang, J. Electrochem. Soc. 157, H27 (2010). 
6. Ming Zhu, Hock-Chun Chin, Ganesh S. Samudra, and 
Yee-Chia Yeo, J. Electrochem. Soc. 155, H76 (2008). 
7. A. Christou, W. T. Anderson Jr., J. E. Davey, M. L. Bark, 
and Y. Anand, Electron. Lett. 16, 254 (1980). 
8. V. F. Mitin, Yu. A. Tkhorik, and E. F. Venger, Microelec-
tron. J. 28, 617 (1997). 
9. V. F. Mitin, P. C. McDonald, F. Pavese, N. S. Boltovets, V. 
V. Kholevchuk, I. Yu. Nemish, V. V. Basanets, V. K. 
Dugaev, P. V. Sorokin, R. V. Konakova, E. F. Venger, and 
E. V. Mitin, Cryogenics 47, 474 (2007). 
10. P. Kostamo, A. Saynatjoki, L. Knuuttila, H. Lipsanen, H. 
Andersson, K. Banzuzi, S. Nenonen, H. Sipila, S. Vaijarvi, 
D. Lumb, Nucl. Instrum. Meth. A 563, 17 (2006). 
11. N. Chand, J. Klem, and H. Morkoç, Appl. Phys. Lett. 48, 
484 (1986). 
12. K. W. Goossen, J. Kolodzey, M. W. Dashiell, and T. Adam, 
in Integrated Photonics Research, A. Sawchuk, ed., 78 of 
OSA Trends in Optics and Photonics (Optical Society of 
America, 2002), paper PD1. 
13. Rajni Gautam, Manoj Saxena, R. S. Gupta, and Mridula 
Gupta, AIP Conf. Proc. 1391, 232 (2011). 
14. O. G. Alaverdova, M. Ya. Fuks, L. S. Khazan, L. P. Koval, 
L. A. Matveeva, I. F. Mikhailov, N. N. Soldatenko, 
Yu. A. Tkhorik, phys. status solidi a 75, 367 (1983). 
15. S. A. Papazian and A. Reisman, J. Electrochem. Soc. 115, 
961 (1968). 
16. W. F. Tseng, J. E. Davey, A. Christou, and B. R. Wilkins, 
Appl. Phys. Lett. 36, 435 (1980). 
17. M. Kawanaka and J. Sone, J. Cryst. Growth 95, 421 (1989). 
18. T. V. Belousova, T. I. Kitaeva, Yu. G. Sadof’ev, and A. B. 
Tolstoguzov, Poverkhnost 6, 60 (1991). 
19. A. L. Demirel, S. Strite, A. Agarwal, M. S. Unlu, H. 
Morkoç, and A. Rockett, J. Vac. Sci. Technol. B 10(2), 664 
(1992). 
20. A. Leycuras and M. G. Lee, Appl. Phys. Lett. 65, 2296 (1994). 
21. B. Salazar-Hernandez, M. A. Vidal, H. Navarro-Contreras, 
and C. Vazquez-Lopez, Thin Solid Films 352, 269 (1999). 
22. M. Bosi, G. Attolini, C. Ferrari, C. Frigeri, . Calicchio, F. 
Rossi, K. Vad, A. Csik, and Z. Zolnai, J. Cryst. Growth 
318, 367 (2011). 
23. Yu Bai, Mayank T. Bulsara, and Eugene A. Fitzgerald, J. 
Appl. Phys. 111, 013502 (2012). 
24. N. P. Garbar, L. A. Matveeva, V. F. Mitin, Yu. A. Tkhorik, 
R. Harman, Yu. M. Shvarts, and Z. Stroubek, Sov. Phys. 
Semicond. 21, 245 (1987). 
25. V. F. Mitin, Appl. Phys. Lett. 92, 202111 (2008). 
26. V. F. Mitin, J. Appl. Phys. 107, 033720 (2010). 
27. V. F. Mitin, V. K. Lazarov, P. M. Lytvyn, P. J. Hasnip, 
V. V. Kholevchuk, L. A. Matveeva, E. Yu. Kolyadina, 
I. E. Kotenko, V. V. Mitin, and E. F. Venger, Phys. Rev. B 
84, 125316 (2011). 
 V.V. KHOLEVCHUK, V.P. KLADKO, A.V. KUCHUK, ET. AL PROC. NAP 2, 01PCSI20 (2013) 
 
 
01PCSI20-4 
28. R. L. Anderson, Solid-State Electron. 5, 341 (1962). 
29. J. Falta, M. C. Reuter, R. M. Tromp, Appl. Phys. Lett. 65, 
1680 (1994). 
30. X.-S. Wang, K. W. Self, and W. H. Weinberg, J. Vac. Sci. 
Technol. A 12, 1920 (1994). 
31. X.-S. Wang, K. Self, V. Bressler-Hill, R. Maboudian, and 
W. H. Weinberg, Phys. Rev. B 49, 4775 (1994). 
32. J. H. Neave, P. K. Larsen, B. A. Joyce, J. P. Gowers, and  
J. F. van der Veen, J. Vac. Sci. Technol. B 1, 668 (1983). 
33. V. Emiliani, A. I. Shkrebtii, C. Goletti, A. M. Frisch, B. O. 
Fimland, N. Esser, and W. Richter, Phys. Rev. B 59, 10657 
(1999). 
34. D. Eres, D. H. Lowndes, J. Z. Tischler, J. W. Sharp,  
T. E. Haynes, and M. F. Chisholm, J. Appl. Phys. 67, 1361 
(1990). 
35. I. Goldfarb, J. L. Azar, A. Grisaru, E. Grunbaum, and M. 
Nathan, J. Appl. Phys. 93, 3057 (2003). 
36. V. I. Vdovin, L. A. Matveeva, G. N. Semenova, M. Ya. 
Skorohod, Yu. A. Tkhorik, L. S. Khazan, phys. status solidi 
a 92, 379 (1985). 
37. B. Jenichen, V. M. Kaganer, R. Shayduk, W. Braun, and 
A. Trampert, phys. status solidi a 206, 1740 (2009). 
38. Chin-An Chang, J. Appl. Phys. 53, 1253 (1982). 
39. Chin-An Chang and Tung-Sheng Kuan, J. Vac. Sci. Tech-
nol. B 1, 315 (1983). 
40. Shih-Hsuan Tang, Edward Yi Chang, Mantu Hudait, Jer-
Shen Maa, Chee-Wee Liu, Guang-Li Luo, Hai-Dang Trinh, 
and Yung-Hsuan Su, Appl. Phys. Lett. 98, 161905 (2011). 
41. A. Leycuras, M. G. Lee, and A. Hausmann, J. Appl. Phys. 
78, 5680 (1995). 
42. G. Attolini, M. Bosi, M. Calicchio, O. Martinez, V. Hortelano, 
Surf. Sci. 606, 808 (2012). 
43. Yu Bai, Kenneth E. Lee, Chengwei Cheng, Minjoo L. Lee, 
Eugene A. Fitzgerald, J. Appl. Phys. 104, 084518 (2008). 
44. L. I. Datsenko, A. P. Klimenko, L. A. Matveeva, I. V. Pro-
kopenko, Yu. A. Tkhorik, Thin Solid Films 33, 275 (1976). 
45. E. Yu. Brailovskii, L. A. Matveeva, G. N. Semenova, 
Yu. A. Tkhorik, L. S. Khazan, phys. status solidi a 66, K59 
(1981). 
46. A. P. Klimenko, L. A. Matveeva, and Yu. A. Tkhorik, 
Czech. J. Phys. B 24, 1139 (1974). 
47. A. L. Aseev, Yu. N. Pogorelov, S. I. Stenin, and V. N. Shum-
sky, Thin Solid Films 32, 351 (1976). 
48. V. Rybka, Z. Sevcik, P. Krejci, and E. Dudrova, Thin Solid 
Films 9, 83 (1972). 
49. M. Dubey, K. A. Jones, W. Y. Han, L. C. West, C. W. Rob-
erts, J. P. Dunkel, L. Peticolas and J. C. Bean, J. Appl. 
Phys. 79, 7157 (1996). 
50. D. Eres, D. H, Lowndes, and J. Z, Tischler, Appl. Phys. 
Lett. 55(10), 1008 (1989)   
51. D. Eres, D. H. Lowndes, J. Z. Tischler, J. W. Sharp,  
T. E. Haynes, M. F. Chisholm, J. Appl. Phys. 67, 1361 (1990). 
52. V.F. Mitin, P.M. Lytvyn, V.V. Kholevchuk, L.A. Matveeva, 
V.V. Mitin, O.S. Kulyk, E.F. Venger, Proc. NAP 1 No3, 
03TF17(4pp) (2012). 
53. G. G. Stoney, Proc. R. Soc. London, Ser. A 82, 172 (1909). 
54. B. L. Freund, S. Suresh, Thin Film Materials; Stress, De-
fect Formation and Surface Evolution (Cambridge Univer-
sity Press, Cambridge, UK, 2004). 
 


Study of Structure and Intrinsic Stresses of Ge Thin Films on GaAs

Electronic Sumy State University Institutional Repository

PROCEEDINGS OF THE INTERNATIONAL CONFERENCE  NANOMATERIALS: APPLICATIONS AND PROPERTIES Vol. 2 No 1, 01PCSI20(4pp) (2013)   2304-1862/2013/2(1)01PCSI20(4) 01PCSI20-1  2013 Sumy State University Study of Structure and Intrinsic Stresses of Ge Thin Films on GaAs  V.V. Kholevchuk, V.P. Kladko, A.V. Kuchuk, P.M. Lytvyn, L.A. Matveeva, V.F. Mitin*  V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine, 03028 Kyiv, Ukraine  (Received 13 June 2013; published online 01 September 2013)  The effect of film growth rate on the structure and intrinsic stresses of thin ( 100 nm) Ge films grown on GaAs(100) substrates was investigate by High Resolution X-Ray Diffraction (HRXRD). The Ge films were deposited onto GaAs using thermal evaporation of Ge in the vacuum. It was shown that pseudomor-phic films with good structural quality can be obtained by this growth technique. We found out that the films have biaxial deformations due to coherent interface and Poisson ratio. The films are elastically com-pressed in the interface and stretched in the perpendicular [001] direction. The intrinsic deformations of thin Ge films strongly depended on the deposition rate. Their correlations with surface roughness, electri-cal and optical parameters are discussed.  Keywords: Ge/GaAs, High resolution X-ray diffraction, Intrinsic stresses   PACS numbers: 61.05.cp, 68.55.− a                                                             * mitin@isp.kiev.ua; mitin@microsensor.com.ua  1. INTRODUCTION  The Ge/GaAs heterostructure is promising for a number of practical applications such as high-performance solar cells [1-4], metal oxide semiconduc-tor field-effect transistors [5, 6], microwave diodes [7], and sensors, e.g. thermometers [8, 9], and -ray and op-tical radiation detectors [8, 10-13]. In addition the Ge/GaAs is an excellent model system for IV/III-V het-erostructures in general. This heterostructure is char-acterized by close values of the components lattice con-stants as well as practical coincidence of their thermal expansion coefficients [1]. These properties are favora-ble for epitaxial growth and fabrication of films and heterojunctions with almost perfect structure. The defect formation in the Ge/GaAs heterostruc-tures depends on which material serves as the sub-strate (Ge or GaAs). In this work, we consider Ge film epitaxy on the GaAs(100) substrate. The Ge lattice constant exceeds that of GaAs. Therefore, the Ge films grown on GaAs substrates are compressed. It was experimentally shown [14] that elastically compressed Ge films on GaAs may exist up to film thickness of 5 m. In that case, there are no mismatch dislocations which could impair the electrical properties of the heterojunction. Thus, it is possible to form a high-quality interface (without misfit disloca-tions) in the Ge/GaAs heterostructure. The distinguishing feature of Ge films on GaAs is the strong dependence of their structural, electrical and optical properties, on the method of preparation. This is related to possible interdiffusion of the joining materials [15-23]. For Ge films, diffused Ga and As at-oms act as shallow acceptors and donors, respectively. Therefore, because of autodoping, the Ge films on GaAs may be p- or n-type with different degrees of compensa-tion including fully compensated [8, 24-27]. Moreover the degree of structural perfection of the Ge films, as well as the concentration of structural defects in them, is determined by the film preparation condition. The Ge films can be amorphous, poly- or single crystalline, with different degrees of structural perfection. The pioneer work on fabrication and investigation of the Ge/GaAs heterostructure can be traced to the paper by Anderson [28]. A rather large number of stud-ies has been done to understand the effect of factors such as: preparation methods, substrate temperature, film thickness and GaAs surface preparation on the growth mechanism [29-37], surface and heterobounda-ry morphology [15, 23, 36-43], intrinsic stresses [12, 33, 39-42], electrical [15, 23, 28, 40, 46-48] and optical [23, 28, 46, 49] properties of Ge films on GaAs. However, the effect of the deposition rate on the prop-erties of Ge films on GaAs remains not fully explored, with few studies considering only high deposition rates [50, 51]. In our previous [8, 24] and recent work [26, 27, 52] we show that deposition rate drastically affects the electrical and optical properties as well as surface mor-phology of thin ( 100 nm) Ge films on GaAs. In particu-lar we show that efficient control of the film properties can be achieved by varying their deposition rate. The subject of this paper is further in-depth study the effect of film growth rate with focus on structure and intrinsic stresses of thin Ge films by using High Resolution X-Ray Diffraction (HRXRD). Measured rocking curves show that pseudomorphic samples with good structural quality can be obtained by this growth technique. It was also shown that the films are elas-tically compressed and intrinsic stresses strongly de-pended on the deposition rate.   2. PREPARATION CONDITIONS AND  MEASUREMENT PROCEDURE  The Ge films were deposited using thermal evapo-ration of Ge in the vacuum (2×10-4 Pa) onto semi-insulating (107 cm) GaAs(100) substrates. The tem-perature of GaAs substrate during the film deposition was maintained at 500 C. The film deposition rate was maintained constant over the course of each deposition; and varied (0.02 0.35) nm/s for different specimens. The evaporation source was a glass-graphite crucible  V.V. KHOLEVCHUK, V.P. KLADKO, A.V. KUCHUK, ET. AL PROC. NAP 2, 01PCSI20 (2013)   01PCSI20-2 heated with electric current flowing through it. The deposition rate was set by the crucible current that determined the Ge evaporation temperature. The film thicknesses were 100±20 nm. Before Ge film deposi-tion, the GaAs substrates were treated with the H2SO4:H2O2:H2O = 4:1:1 etchant for 3 min. and ther-mal annealed in vacuum at 500 С for 15 min. The structural quality of Ge/GaAs heterostructure was studied by HRXRD using a Philips MRD diffrac-tometer with a Cu anode X-ray beam. The X-ray source was operated at 40 kV and 40 mA. A four-crystal Bar-tels monochromator was employed using four Ge 022 reflections to provide a monochromatic beam with a divergence of 12 arcsec.  The intrinsic stresses (σ) due to lattice mismatch between Ge and GaAs also were determined from the radius of curvature of specimen surfaces using a profil-ograph and by application of the Stoney’s formula [53, 54], 2 [6(1 ) ]Et Rd  where E, t and ν are Young’s modulus, thickness and Poisson ratio of the substrate, respectively, d is the film thickness and R is the heterosystem bending radius.  3. EXPERIMENTAL RESULTS AND DISCUS-SION  3.1 Structure and Intrinsic Stresses  Fig. 1 shows the experimental and simulated rock-ing curves (004 reflection) for Ge/GaAs films obtained at different growth rates. One can clearly observe the Bragg peaks for Ge and GaAs substrate. The Ge films are pseudomorphic. The in-plane Ge lattice constant is very close to that of GaAs, with corresponding lattice constant increasing in the perpendicular direction. The left-side shift of Ge film maximum in comparison with a bulk Ge single crystal is observed (Fig. 1). The verti-cal dotted lines in Fig. 1 indicate the diffraction angle position for bulk Ge. At low deposition rate, the absence of interference fringes and higher intensity of tails are caused by some structural inhomogeneities of the film and interface roughness that were not taken into account at simula-tions. At high growth rate, the interference fringes in the Ge film are observed (Fig. 1(b)), thus indicating phase coherency of the diffracted waves and high crystalline quality of this heterostructure.  The investigations of radius of curvature of the Ge/GaAs heterostructure showed that Ge films are compressed. The intrinsic stresses in the Ge films about 100 nm thick also calculated using the Stoney’s formula are at the level of several tenth parts of GPa. They depend on the film growth rate, decreasing from 6.7 108 Pa to 2 108 Pa (i.e. by more than three times) as the deposition rate decreased from 0.35 nm/s to 0.02 nm/s (Fig. 2).  3.2 Surface Roughness, Electrical and Optical Parameters  In our recent work [27, 52] we show that deposition rate also strongly affects the surface morphology, elec-trical and optical properties of the Ge films.    Fig. 1 – Rocking curves (004) for Ge films on GaAs. The film thickness was 100±20 nm. Ge growth deposition rates used are 0.02 nm/s (a) and 0.35 nm/s (b). Vertical dotted line denotes position of diffraction maximum from the bulk Ge. Simulated dotted curves correspond to ideally pseudomorphic film. The blue curve in (b) is simulation fitted to experimental data     Fig. 2 – Dependence of intrinsic stresses ( ) in Ge films on GaAs on the film growth rate (V). The film thickness was con-stant (about 130 nm)  The films prepared at high deposition rate have smooth surfaces with root-mean-square (RMS) rough-ness of about 0.5 nm. In contrast, at low growth rate film roughness is large and can reach up to 14.6 nm in the film of 100 nm thick.  STUDY OF STRUCTURE AND INTRINSIC STRESSES … PROC. NAP 2, 01PCSI20 (2013)   01PCSI20-3 Optical absorption measurements of the Ge films show that at energies E < Eg, the optical absorption coefficient D depends on the photon energy E as ]/)(exp[ EED g , where   dE/dlnD  is the charac-teristic energy that determines the spreading of the fundamental absorption edge. For the Ge films in this study  does not depend on temperature. This exponen-tial dependence D(E) is related to the tails in the densi-ty-of-states in the Ge band gap. The existence of these tails permits optical transitions at photon energies be-low Eg. Table 1 presents the  values for films obtained at different deposition rates. As the deposition rate decreased, the tails in the density of states, and there-by the  value, increased. The degree of spreading of the fundamental absorption edge  can be varied from 60 meV up to 140 meV.  Table 1 – Dependencies of intrinsic stresses ( ), characteristic energy , resistivity ( ), activation energy of conductivity (ε1), conductivity type and root-mean-square (RMS) roughness for the Ge films of 100±20 nm thicknesses grown at different dep-osition rates V.  V (nm/s) 0.02 0.35  (Pa) 2 108 6.7 108 RMS (nm) 14.6 0.49  ( /cm) 120 0.02 1 (eV) 0.35 0 Conductivity type p n  (meV) 140 70 The transport phenomena in Ge films obtained at low and high deposition rate also differ drastically. The Ge films obtained at high deposition rate are n-type, low-resistant (0.1-0.01 cm), heavily doped and slight-ly compensated (Table 1). Temperature dependence of conductivity in these films is weak or practically ab-sent. The films obtained at low deposition rate are p-type, high-resistant ( 100 cm), heavily doped, and strongly compensated; in the limiting case fully com-pensated. Their conductivity is thermally activated. The activation energy of conductivity can reach up to half of the Ge band gap (Table 1).  4. CONCLUSION  We present a HRXRD study of Ge/GaAs thin films. The measured rocking curves show that an ideally pseudomorphic growth of Ge films with good single crystal structure can be obtained by this growth tech-nique. The film-substrate interface is coherent and dis-location free. It was also shown that the films are elas-tically compressed and intrinsic stresses strongly de-pend on the deposition rate. This effect is essential and should be taken into account when developing and pro-ducing devices based on the Ge/GaAs heterostructure.  AKNOWLEDGEMENTS  This work was partially funded under the Ukraini-an State Program “Nanotechnologies and nanomateri-als”, Projects No. 2.2.6.15 and 3.6.1.10.     REFERENCES  1. G. Milnes and D. L. Feucht, Heterojunctions and Metal-Semiconductor Junctions (Academic, New York, 1972). 2. M. Meyer, and R. A. Metzger, Compnd. Semicond. 2, 22 (1996). 3. C. Flores, B. Bollani, R. Campensato, D. Passoni, and G. L. Timò, Microelectron. Eng. 18, 175 (1992). 4. S. J. Wojtczuk, S. P. Tobin, C. J. Keavney, C. Bajgar, M. M. Sanfacon, L. M. Geoffroy, T. M. Dixon, S. M. Vernon, J. D. Scofield, and D. S. Ruby, IEEE T. Elec-tron. Dev. 37, 455 (1990). 5. G.-L. Luo, Z.-Y. Han, C.-H. Chien, C.-H. Ko, C. H. Wann, H.-Y. Lin, Y.-L. Shen, C.-T. Chung, S.-C. Huang, C.-C. Cheng, and C.-Y. Chang, J. Electrochem. Soc. 157, H27 (2010). 6. Ming Zhu, Hock-Chun Chin, Ganesh S. Samudra, and Yee-Chia Yeo, J. Electrochem. Soc. 155, H76 (2008). 7. A. Christou, W. T. Anderson Jr., J. E. Davey, M. L. Bark, and Y. Anand, Electron. Lett. 16, 254 (1980). 8. V. F. Mitin, Yu. A. Tkhorik, and E. F. Venger, Microelec-tron. J. 28, 617 (1997). 9. V. F. Mitin, P. C. McDonald, F. Pavese, N. S. Boltovets, V. V. Kholevchuk, I. Yu. Nemish, V. V. Basanets, V. K. Dugaev, P. V. Sorokin, R. V. Konakova, E. F. Venger, and E. V. Mitin, Cryogenics 47, 474 (2007). 10. P. Kostamo, A. Saynatjoki, L. Knuuttila, H. Lipsanen, H. Andersson, K. Banzuzi, S. Nenonen, H. Sipila, S. Vaijarvi, D. Lumb, Nucl. Instrum. Meth. A 563, 17 (2006). 11. N. Chand, J. Klem, and H. Morkoç, Appl. Phys. Lett. 48, 484 (1986). 12. K. W. Goossen, J. Kolodzey, M. W. Dashiell, and T. Adam, in Integrated Photonics Research, A. Sawchuk, ed., 78 of OSA Trends in Optics and Photonics (Optical Society of America, 2002), paper PD1. 13. Rajni Gautam, Manoj Saxena, R. S. Gupta, and Mridula Gupta, AIP Conf. Proc. 1391, 232 (2011). 14. O. G. Alaverdova, M. Ya. Fuks, L. S. Khazan, L. P. Koval, L. A. Matveeva, I. F. Mikhailov, N. N. Soldatenko, Yu. A. Tkhorik, phys. status solidi a 75, 367 (1983). 15. S. A. Papazian and A. Reisman, J. Electrochem. Soc. 115, 961 (1968). 16. W. F. Tseng, J. E. Davey, A. Christou, and B. R. Wilkins, Appl. Phys. Lett. 36, 435 (1980). 17. M. Kawanaka and J. Sone, J. Cryst. Growth 95, 421 (1989). 18. T. V. Belousova, T. I. Kitaeva, Yu. G. Sadof’ev, and A. B. Tolstoguzov, Poverkhnost 6, 60 (1991). 19. A. L. Demirel, S. Strite, A. Agarwal, M. S. Unlu, H. Morkoç, and A. Rockett, J. Vac. Sci. Technol. B 10(2), 664 (1992). 20. A. Leycuras and M. G. Lee, Appl. Phys. Lett. 65, 2296 (1994). 21. B. Salazar-Hernandez, M. A. Vidal, H. Navarro-Contreras, and C. Vazquez-Lopez, Thin Solid Films 352, 269 (1999). 22. M. Bosi, G. Attolini, C. Ferrari, C. Frigeri, . Calicchio, F. Rossi, K. Vad, A. Csik, and Z. Zolnai, J. Cryst. Growth 318, 367 (2011). 23. Yu Bai, Mayank T. Bulsara, and Eugene A. Fitzgerald, J. Appl. Phys. 111, 013502 (2012). 24. N. P. Garbar, L. A. Matveeva, V. F. Mitin, Yu. A. Tkhorik, R. Harman, Yu. M. Shvarts, and Z. Stroubek, Sov. Phys. Semicond. 21, 245 (1987). 25. V. F. Mitin, Appl. Phys. Lett. 92, 202111 (2008). 26. V. F. Mitin, J. Appl. Phys. 107, 033720 (2010). 27. V. F. Mitin, V. K. Lazarov, P. M. Lytvyn, P. J. Hasnip, V. V. Kholevchuk, L. A. Matveeva, E. Yu. Kolyadina, I. E. Kotenko, V. V. Mitin, and E. F. Venger, Phys. Rev. B 84, 125316 (2011).  V.V. KHOLEVCHUK, V.P. KLADKO, A.V. KUCHUK, ET. AL PROC. NAP 2, 01PCSI20 (2013)   01PCSI20-4 28. R. L. Anderson, Solid-State Electron. 5, 341 (1962). 29. J. Falta, M. C. Reuter, R. M. Tromp, Appl. Phys. Lett. 65, 1680 (1994). 30. X.-S. Wang, K. W. Self, and W. H. Weinberg, J. Vac. Sci. Technol. A 12, 1920 (1994). 31. X.-S. Wang, K. Self, V. Bressler-Hill, R. Maboudian, and W. H. Weinberg, Phys. Rev. B 49, 4775 (1994). 32. J. H. Neave, P. K. Larsen, B. A. Joyce, J. P. Gowers, and  J. F. van der Veen, J. Vac. Sci. Technol. B 1, 668 (1983). 33. V. Emiliani, A. I. Shkrebtii, C. Goletti, A. M. Frisch, B. O. Fimland, N. Esser, and W. Richter, Phys. Rev. B 59, 10657 (1999). 34. D. Eres, D. H. Lowndes, J. Z. Tischler, J. W. Sharp,  T. E. Haynes, and M. F. Chisholm, J. Appl. Phys. 67, 1361 (1990). 35. I. Goldfarb, J. L. Azar, A. Grisaru, E. Grunbaum, and M. Nathan, J. Appl. Phys. 93, 3057 (2003). 36. V. I. Vdovin, L. A. Matveeva, G. N. Semenova, M. Ya. Skorohod, Yu. A. Tkhorik, L. S. Khazan, phys. status solidi a 92, 379 (1985). 37. B. Jenichen, V. M. Kaganer, R. Shayduk, W. Braun, and A. Trampert, phys. status solidi a 206, 1740 (2009). 38. Chin-An Chang, J. Appl. Phys. 53, 1253 (1982). 39. Chin-An Chang and Tung-Sheng Kuan, J. Vac. Sci. Tech-nol. B 1, 315 (1983). 40. Shih-Hsuan Tang, Edward Yi Chang, Mantu Hudait, Jer-Shen Maa, Chee-Wee Liu, Guang-Li Luo, Hai-Dang Trinh, and Yung-Hsuan Su, Appl. Phys. Lett. 98, 161905 (2011). 41. A. Leycuras, M. G. Lee, and A. Hausmann, J. Appl. Phys. 78, 5680 (1995). 42. G. Attolini, M. Bosi, M. Calicchio, O. Martinez, V. Hortelano, Surf. Sci. 606, 808 (2012). 43. Yu Bai, Kenneth E. Lee, Chengwei Cheng, Minjoo L. Lee, Eugene A. Fitzgerald, J. Appl. Phys. 104, 084518 (2008). 44. L. I. Datsenko, A. P. Klimenko, L. A. Matveeva, I. V. Pro-kopenko, Yu. A. Tkhorik, Thin Solid Films 33, 275 (1976). 45. E. Yu. Brailovskii, L. A. Matveeva, G. N. Semenova, Yu. A. Tkhorik, L. S. Khazan, phys. status solidi a 66, K59 (1981). 46. A. P. Klimenko, L. A. Matveeva, and Yu. A. Tkhorik, Czech. J. Phys. B 24, 1139 (1974). 47. A. L. Aseev, Yu. N. Pogorelov, S. I. Stenin, and V. N. Shum-sky, Thin Solid Films 32, 351 (1976). 48. V. Rybka, Z. Sevcik, P. Krejci, and E. Dudrova, Thin Solid Films 9, 83 (1972). 49. M. Dubey, K. A. Jones, W. Y. Han, L. C. West, C. W. Rob-erts, J. P. Dunkel, L. Peticolas and J. C. Bean, J. Appl. Phys. 79, 7157 (1996). 50. D. Eres, D. H, Lowndes, and J. Z, Tischler, Appl. Phys. Lett. 55(10), 1008 (1989)   51. D. Eres, D. H. Lowndes, J. Z. Tischler, J. W. Sharp,  T. E. Haynes, M. F. Chisholm, J. Appl. Phys. 67, 1361 (1990). 52. V.F. Mitin, P.M. Lytvyn, V.V. Kholevchuk, L.A. Matveeva, V.V. Mitin, O.S. Kulyk, E.F. Venger, Proc. NAP 1 No3, 03TF17(4pp) (2012). 53. G. G. Stoney, Proc. R. Soc. London, Ser. A 82, 172 (1909). 54. B. L. Freund, S. Suresh, Thin Film Materials; Stress, De-fect Formation and Surface Evolution (Cambridge Univer-sity Press, Cambridge, UK, 2004).  

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Study of Structure and Intrinsic Stresses of Ge Thin Films on GaAs

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