Collin Hitchcock

Ternary and quaternary antimonide devices for thermophotovoltaic applications

Thermophotovoltaic (TPV) devices have been fabricated using epitaxial ternary and quaternary layers grown on GaSb substrates. GaInSb ternary devices were grown by metalorganic vapor phase epitaxy (MOVPE) with buffer layers to accommodate the lattice mismatch, and GaInAsSb lattice-matched quaternaries were grown by MOVPE and by liquid phase epitaxy (LPE). Improved devices are obtained when optical absorption occurs in the p-layer due to the longer minority carrier diffusion length. Thick emitter p/n devices are limited by surface recombination, with highest quantum efficiency and lowest dark current being achieved with epitaxially grown surface passivation layers on lattice-matched MOVPE quaternaries. Thin emitter/thick base n/p devices are very promising, but require improved shallow high-quality n-type ohmic contacts.

Growth and characterization of In0.2Ga0.8Sb device structures using metalorganic vapor phase epitaxy

In0.2Ga0.8Sb epitaxial layers and thermophotovoltaic (TPV) device structures have been grown on GaSb and GaAs substrates by metalorganic vapor phase epitaxy (MOVPE). Control of the n-type doping up to 1×1018 cm−3 was achieved using diethyltellurium (DETe) as the dopant source. A Hall mobility of greater than 8000 cm2/Vs at 77K was obtained for a 3×1017 cm−3 doped In0.2Ga0.8Sb layer grown on high-resistivity GaSb substrate. The In0.2Ga0.8Sb epilayers directly grown on GaSb substrates were tilted with respect to the substrates, with the amount of tilt increasing with the layer thickness. Transmission electron microscopy (TEM) studies of the layers showed the presence of dislocation networks across the epilayers parallel to the interface at different distances from the interface, but the layers above this dislocation network were virtually free of dislocations. A strong correlation between epilayer tilt and TPV device properties was found, with layers having more tilt providing better devices. The results su...

p-Type and n-type doping in GaSb and Ga0.8In0.2Sb layers grown by metalorganic vapor phase epitaxy

P-type and n-type GaSb and GA{sub 0.8}In{sub 0.2}Sb layers have been grown on GaSb and GaAs substrates by metalorganic vapor phase epitaxy (MOVPE) using silane and diethyltellurium (DETe) as the dopant precursors, respectively. Hall measurements show that the concentration and mobility of holes and electrons in GaSb and GA{sub 0.8}In{sub 0.2}Sb are higher when the layers are grown on GaSb substrates than when grown on GaAs substrates. Secondary ion mass spectrometry (SIMS) results show that the incorporation of Si and Te is higher when GaSb substrates are used. The electron concentration increased from 5 {times} 10{sup 16} cm{sup {minus}3} to 1.5 {times} 10{sup 18} cm{sup {minus}3} as the Te concentration was increased from 1 {times} 10{sup 17} cm{sup {minus}3} to 5 {times} 10{sup 18} cm{sup {minus}3}. As the Te concentration was increased further, the electron concentration decreased, with only about 1% of the Te electrically active at a Te concentration of 2 {times} 10{sup 20} cm{sup {minus}3}.

Antimonide-based devices for thermophotovoltaic applications

Thermophotovoltaic (TPV) devices have been fabricated using ternary and quaternary layers grown by metalorganic vapor phase epitaxy (MOVPE) on GaSb substrates. GaInSb ternary devices were grown with buffer layers to accommodate the lattice mismatch, and GaInAsSb quaternary devices were grown with lattice-matched compositions. Improved devices are obtained when optical absorption occurs in the p-layer due to the longer minority carrier diffusion length. Thick emitter p/n devices are limited by surface recombination, with highest quantum efficiency and lowest dark current being achieved with epitaxially grown surface passivation layers on lattice-matched MOVPE quaternaries. Thin emitter/thick base, n/p devices are very promising since surface passivation is less critical than for p-emitter devices.

4H-SiC n-Channel Insulated Gate Bipolar Transistors on (0001) and (000-1) Oriented Free-Standing n − Substrates

We experimentally demonstrate 4H-SiC n-channel, planar gate insulated gate bipolar transistors (IGBTs) on 180-μm thick lightly doped free-standing n- substrates with ion-implanted collector regions, and metal-oxide-semiconductor gates on (0001) and (000-1) surfaces. The IGBTs show an ON-state current density of 20 A/cm2 at a power dissipation of 300 W/cm2. The threshold voltages are measured to be 7.5 V and 10.5 V on Si-face and C-face, respectively. Both IGBTs show a small positive temperature coefficient of the forward voltage drop, which is useful for easy parallelization of devices.

1200V, 25A bi-directional Si DMOS IGBT fabricated with fusion wafer bonding

A 1200V, 25A bi-directional silicon DMOS-IGBT has been successfully fabricated using a hydrophobic bonding process at low temperature (400°C). With the aid of a glass carrier approach, a flat and clean bonding surface for producing an electrically stable and transparent junction was achieved. The static and dynamic performance with and without back-side gate control are presented and compared.

Experimental Demonstration of High-Voltage 4H-SiC Bi-Directional IGBTs

We experimentally demonstrate, for the first time, bi-directional 4H-SiC planar gate, insulated gate bipolar transistors fabricated on 250-μm thick, lightly doped free-standing substrates. On Si face, forward voltage drop (at 50 A/cm2) of 9.7 V was obtained at room temperature, with a differential ON-resistance of 140 mQ · cm2, indicating good conductivity modulation. We have also demonstrated control over minority carrier injection in static characteristics of the BD-IGBTs by application of a back-gate bias.

Characteristics of 4H-SiC P-i-N diodes on lightly doped free-standing substrates

This paper presents static and dynamic electrical characteristics of implanted 4H-SiC PiN diodes fabricated on Si-face and C-face of lightly doped free-standing substrates. The device performance is found to be comparable to conventional diodes. Carrier lifetime of about 2.5 μs was measured for the drift region.

GaInSb and GaInAsSb thermophotovoltaic device fabrication and characterization

Thermophotovoltaic (TPV) devices have been fabricated using epitaxial ternary and quaternary layers grown on GaSb substrates. The GaInSb layers were grown by organometallic vapor phase epitaxy (OMVPE) and the InGaAsSb lattice-matched layers were grown by liquid phase epitaxy (LPE). Device fabrication steps include unannealed p-type ohmic contacts, annealed Sn/Au n-type ohmic contacts, and a thick Ag top-surface contact using a lift-off process. Devices are characterized primarily by dark I-V, photo I-V, and quantum efficiency measurements, which are correlated to microscopic and macroscopic material properties. Particular emphasis has been on material enhancements to increase quantum efficiency and decrease dark saturation current density. TPV device performance is presently limited by the base diffusion length, typically 1 to 2 microns.

Characteristics of GaSb and GaInSb layers grown by metalorganic vapor phase epitaxy

GaInSb and GaSb layers have been grown on GaSb and GaAs substrates using metalorganic vapor phase epitaxy (MOVPE) with trimethylgallium, trimethylindium and trimethylantimony as the sources. As grown layers are p type with the carrier concentration in the mid 10{sup 16} cm{sup {minus}3} range. N type layers are grown using diethyltellurium as the Te source. Incorporation of Te in high concentration showed compensation and secondary ion mass spectrometry (SIMS) result showed that only 2.5% of Te are active when 2 {times} 10{sup 19} cm{sup {minus}3} of Te was incorporated. The carrier concentration measured in n type samples increases as the temperature is lowered. This is explained by the presence of second band close to the conduction band minima. Silane which is a common n type dopant in GaAs and other III-V systems is shown to behave like p type in GaInSb. P-n junction structures have been grown on GaSb substrates to fabricate TPV cells.