Heavy p-type carbon doping of MOCVD GaAsP using CBrCl₃

CBrCl₃ is shown to be a useful precursor for heavy p-type carbon doping of GaAsxP1−x grown via metalorganic chemical vapor deposition (MOCVD) across a range of compositions. Structural and electrical properties of the GaAsP films were measured for various processing conditions. Use of CBrCl3 decreased the growth rate of GaAsP by up to 32% and decreases x by up to 0.025. The dependence of these effects on precursor inputs is investigated, allowing C-doped GaAsP films to be grown with good thickness and compositional control. Hole concentrations of greater than 2×10¹⁹ cm−3 were measured for values of x from 0.76 to 0.90.National Science Foundation (U.S.) (Award 0939514)National Research Foundation of SingaporeNational Science Foundation (U.S.) (Award DMR-14-19807

GaAsP/InGaP heterojunction bipolar transistors grown by MOCVD

Heterojunction bipolar transistors with GaAs[subscript x]P[subscript 1−x] bases and collectors and In[subscript y]Ga[subscript 1−y]P emitters were grown on GaAs substrates via metalorganic chemical vapor deposition, fabricated using conventional techniques, and electrically tested. Four different GaAs[subscript x]P[subscript 1−x] compositions were used, ranging from x = 0.825 to x = 1 (GaAs), while the In[subscript y]Ga[subscript 1−y]P composition was adjusted to remain lattice-matched to the GaAsP. DC gain close to or exceeding 100 is measured for 60 μm diameter devices of all compositions. Physical mechanisms governing base current and therefore current gain are investigated. The collector current is determined not to be affected by the barrier caused by the conduction band offset between the InGaP emitter and GaAsP base. While the collector current for the GaAs/InGaP devices is well-predicted by diffusion of electrons across the quasi-neutral base, the collector current of the GaAsP/InGaP devices exceeds this estimate by an order of magnitude. This results in higher transconductance for GaAsP/InGaP than would be estimated from known material properties.National Science Foundation (U.S.) (Award 0939514

GaAsP/InGaP heterojunction bipolar transistors for III-V on Si microelectronics

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2017.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student-submitted PDF version of thesis.Includes bibliographical references (pages 129-140).GaAs-based transistors are capable of operating at high frequency with low noise, and are produced in large volumes for a wide range of applications including microwave frequency ICs for input/output in mobile devices. However, Si CMOS still holds an advantage for digital logic due to wide market penetration resulting in decades of development and lower cost. Monolithic integration of III-V analog circuity and Si CMOS gives circuit designers the best of both materials. In addition, by substituting GaAsxP₁-x (0.8 < x < 1) for GaAs as an active material, we can take advantage of its higher breakdown voltage and reduced lattice mismatch with Si. In this thesis, we study GaAsP/InGaP heterojunction bipolar transistors (HBTs) grown via MOCVD as a test-bed for III-V microelectronics integration with Si. Epitaxial challenges involving growth of GaAsP/InGaP HBT structures on Si substrates were addressed. Heavy C p-type doping of GaAsP via MOCVD, necessary for the HBT base region, was studied. Growth rate, composition, and hole concentration dependence on C precursor (CBrCl₃) input was investigated, yielding GaAsP films with hole concentrations in excess of 2 x 10¹⁹ cm-³. GaAs₀₈₂₅P was grown on Si substrates via a SiGe graded buffer with a threading dislocation density of 3.7 x 106 cm-2 measured by PV-TEM and EBIC. This density is appropriate for fabrication of minority-carrier devices such as HBTs. GaAsP/InGaP HBTs were fabricated on both GaAs and Si substrates with a range of defect densities to measure the effect on DC performance and prove the feasibility of GaAsP transistor growth on Si. Models for the effect of threading dislocation density and misfit dislocation density (in the active device layers) on current gain were developed. A GaAsP/InGaP HBT grown on Si was demonstrated with a current gain as high as 158. Changes in GaAsxP₁-x composition from 0.825 < x < 1 did not have a significant effect on current gain. Collector current was determined not to be controlled by thermionic emission of electrons from the emitter into the base, contrary to prior reports. In addition, GaAsP was shown to support a higher breakdown voltage than GaAs, consistent with modeling.by Christopher Heidelberger.Ph. D

Sub-10-nm-Diameter InGaAs Vertical Nanowire MOSFETs: Ni Versus Mo Contacts

Recently, sub-10-nm-diameter InGaAs vertical nanowire (VNW) MOSFETs have been demonstrated. The key to this achievement was the use of Ni for the top ohmic contact. In this paper, we present a detailed study of the impact of Ni and Mo contacts on the electrical characteristics of highly scaled InGaAs VNW MOSFETs. Sequential annealing experiments are presented that reveal the optimum temperature for each type of contact. A negative temperature dependence of the ON-resistance of 7-nm-diameter Ni-contacted devices suggests the existence of an energy barrier. We also observe an unexpected transconductance and drain-induced barrier loweirng (DIBL) dependence on transistor diameter in Ni-contacted devices as well as abnormal DIBL asymmetry to swapping source and drain. All these results can be explained by Ni diffusing down the nanowire during the contact annealing process, reducing the effective channel length, and creating a Schottky-barrier drain

Improved retention of phosphorus donors in germanium using a non-amorphizing fluorine co-implantation technique

Co-doping with fluorine is a potentially promising method for defect passivation to increase the donor electrical activation in highly doped n-type germanium. However, regular high dose donor-fluorine co-implants, followed by conventional thermal treatment of the germanium, typically result in a dramatic loss of the fluorine, as a result of the extremely large diffusivity at elevated temperatures, partly mediated by the solid phase epitaxial regrowth. To circumvent this problem, we propose and experimentally demonstrate two non-amorphizing co-implantation methods; one involving consecutive, low dose fluorine implants, intertwined with rapid thermal annealing and the second, involving heating of the target wafer during implantation. Our study confirms that the fluorine solubility in germanium is defect-mediated and we reveal the extent to which both of these strategies can be effective in retaining large fractions of both the implanted fluorine and, critically, phosphorus donors. \ua9 2017 Author(s)

Heteroepitaxial growth of In 0.30

We report on the growth of an In0.30Ga0.70As channel high-electron mobility transistor (HEMT) on a 200 mm silicon wafer by metal organic vapor phase epitaxy. By using a 3 μm thick buffer comprising a Ge layer, a GaAs layer and an InAlAs compositionally graded strain relaxing buffer, we achieve threading dislocation density of (1.0 ± 0.3) × 107 cm−2 with a surface roughness of 10 nm RMS. No phase separation was observed during the InAlAs compositionally graded buffer layer growth. 1.4 μm long channel length transistors are fabricated from the wafer with IDS of 70 μA/μm and gm of above 60 μS/μm, demonstrating the high quality of the grown materials