Heuken, M.

Jansen, R. A.

Kalisch, H.

Lutsenko, E. V.

Pavlovskii, V. N.

Schineller, B.

Walther, T.

Yablonskii, G. P.

Zubialevich, V. Z.

English

Электронная библиотека БГУ

OPTICAL AND LASER PROPERTIES OF THE ZNSE/ZNMGSSE 
MULTIPLE QUANTUM WELL HETEROSTRUCTURES
G. P. Yablonskii1, E. V. Lutsenko1, V. N. Pavlovskii1, V. Z. Zubialevich1,
H. Kalisch2, R. A. Jansen2, T. Walther3, B. Schineller4, M. Heuken4
1Stepanov Institute of Physics of the NASB, Minsk, Belarus 
2Institut fur Theoretische Elektrotechnik RWTH, Aachen, Germany 
3Institut fur Anorganische Chemie, UniversitAt Bonn, Bonn, Germany 
AIXTRON AG, Aachen, Germany
A pronounced laser threshold and directivity of laser emission having 
TE polarization were observed for the investigated ZnSe/ZnMgSSe MQW- 
SCHs at excitation intensity enhancement. The full width at half-maximum 
(FWHM) of the PL band at the laser threshold was 15 nm and the FWHM 
of the total laser spectrum was 0.5-1 nm. The laser threshold value Ithr was
Л
10-30 kW/cm at RT depending on the cavity length. The laser action was 
observed up to temperatures of 620 K.
A near RT fragment of the temperature dependence of the 
ZnSe/ZnMgSSe MQW-SCH laser spectra at Iexc = 1.1 -Ithr is presented in 
Fig. 1. The total laser spectrum maximum shifts to the long-wave region 
with the temperature enhancement (line 2) whereas the spectral position of 
the individual longitudinal laser mode (line 1) shifts slightly to the short­
wave side. Coefficients of the temperature shift were 0.02 meV/K for the 
individual longitudinal laser mode and -0.55 meV/K for the position of the 
total laser spectrum maximum.
The laser spectra behaviour depending on Iexc is presented in Fig. 2. 
An insignificant short-wave shift of the total laser spectrum maximum
Л
occurs up to intensity of exciting emission of 150 kW/cm (region I) which 
can be attributed to the band filling. A considerable long-wave shift of the
Л
total laser spectrum maximum is observed at Iexc = 150-600 kW/cm 
(region II). The shift can be attributed to the active region heating and 
band gap renormalisation. A comparison of excitation shift with the same 
of temperature gives the maximum value of the active layer overheating of 
about 7 K at Iexc = 600 kW/cm2.
Short-wave shift of the position of the individual modes is of the
Л
order 0.58 meV at Iexc = 70 - 600 kW/cm (Fig. 2) whereas overheating of 
AT=  7 K can lead to the shift of AEmax = 0.02AT = 0.4 meV. Obviously 
the short-wave shift of the individual laser modes is not caused only by 
active region heating but also by the change of the waveguide region 
refractive index. In turn it is due to an revising of the optical confinement
59
factor and the active region refractive index caused by an increase of the 
electron-hole plasma oscillations frequency with pumping increment.
Temperature [K] Excitation Intensity [kW/cm2]
Fig. 1. Normalised laser spectra Fig. 2. Normalised laser spectra of the
depending on temperature for ZnSe/ZnMgSSe MQW-SCH laser as a
ZnSe/ZnMgSSe MQW-SCH laser: 1 -  function of excitation intensity. 1, 3 -
individual laser mode peak position; individual laser mode position, 2 -  position
2 -  total laser spectrum position. of the total laser spectrum maximum.
Strong short-wave shift of both the total laser spectrum and the laser
л
modes position is observed for excitation levels of above 600 kW/cm 
(Fig. 2, region III). It indicates a significant reduction of the refractive 
index of the active region similar to that observed at high-temperature 
degradation [1, 2] with diffusion of the barrier, waveguiding and cladding 
layer components into the active region. This shift is accompanied by an 
irreversible laser emission intensity reduction indicating the intensive 
degradation processes under excitation intensity far above the threshold.
Since overheating of 7 K at RT can not be an origin of the 
degradation process, a series of experiments was carried out on 
determination of the PL and laser spectra and intensity dependence on the 
amount of the exciting pulses in order to establish reasons of degradation. 
Fig. 3 shows the laser spectra of a sample at different excitation levels 
(curves 1-4) and the same measured after irradiation with number of pulses 
N  = 106 at Iexc = 900 kW/cm2. The total laser spectrum after degradation is 
short-wave shifted on about 20 meV comparing to that before degradation. 
Seemingly the large shift is due to formation in the active layers the 
quaternary or ternary compound as a result of the S and/or Mg atoms 
diffusion from the ZnMgSSe layers stimulated by laser light.
In order to clarify the pumping and inherent laser light role in the 
degradation of the ZnSe/ZnMgSSe heterostructures, measurements of the 
laser output and PL intensities (in the lasing absence) as a function of N
60
were carried out at two Iexc 
Wavelength [nm]
465 460
(200 kW/cm2 and 600 kW/cm2, Fig. 4).
455
з
n
V)с<D
со
'55(Л
Ёш
T = 300
As grown 
lscx [kW/cm2] 
- -  -  (1) - 17.5
' .......  (2) - 31.3
-------(3) - 84.6
------- (4) - 200
degradated 
' L y [kW/cm2]
Y - (5) - 200
2.68
3
ri
> 10° -
<лсо■иС
со
'S5
(Л
£
ш
2.70
Energy [eV]
2.72
105
N [pulses]
106
Fig. 3. Laser spectra of as grown (1-4) Fig. 4. PL (1, 2) and laser (3, 4) intensities 
and degraded (5) ZnSe/ZnMgSSe MQW- of ZnSe/ZnMgSSe MQW-SCH as a function 
SCH laser. of number of N2 laser pulses.
PL intensity without lasing in contrast to the laser output power of the 
ZnSe/ZnMgSSe MQW-SCH laser structures does not show any decrease 
with N  rise at the same N  and Iexc. On the contrary, the PL intensity rises 
step by step with N  evidencing of laser annealing of the initial defects as it 
was observed for the bulk crystals [3] and epitaxial layers [4] of ZnSe. This 
fact lets us to assume that namely interaction of inherent ZnSe/ZnMgSSe 
laser emission with the heterostructure layers is the reason of the 
degradation process. The ZnSe based laser energy per pulse was 10 nJ and 
the inherent light intensity in the active layers was estimated to be of about 'j
5 MW/cm , taking into account the optical confinement factor value of 
Г =  0.13 calculated for this structure.
It was shown that the active region of the ZnSe/ZnMgSSe MQW- 
SCH lasers overheating value does not exceed 10 K. A significant decrease 
of the laser power during operation takes place for Iexc = (5-10) Ithr. It was 
shown that the degradation takes place due to action of intrinsic laser 
emission and it is defined seemingly by stimulated diffusion of the 
elements of ZnMgSSe claddings and barriers into the ZnSe active region.
1. Marko I. P., Lutsenko E. V., Yablonskii G. P. et al. // Phys. Stat. Sol. (a). 2001. 
V. 185. P. 301.
2. Walther T.,Kalisch H., Heime K. et al. // Phys. Stat. Sol. (a). 2000. V. 180. P. 351.
3. Yablonskii G. P. // Sov. Phys. - Semicond. 1984. V. 18. P. 570.
4. Yablonskii G. P., Gurskii A. L., Lutsenko E. V. et al. // Phys. Stat. Sol. (a). 1997. 
V. 159. P. 543.
61


Optical and laser properties of the ZnSe/ZnMgSSe multiple quantum well heterostructures

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Optical and laser properties of the ZnSe/ZnMgSSe multiple quantum well heterostructures

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