Kung-Liang Lin

The Roles of Threading Dislocations on Electrical Properties of AlGaN/GaN Heterostructure Grown by MBE

The role played by different types of threading dislocations (TDs) on the electrical properties of AlGaN/GaN heterostructure grown by plasma-assisted molecular beam epitaxy (MBE) was investigated. Samples with different defect structures and densities were prepared and measurements were taken from the same sample to study the correlative behavior of various TDs. From the Hall measurement, the electron mobility in two-dimensional electron gas channel was mainly controlled by the edge dislocation, which has a dominant amount in the material. The edge TDs acted as Coulomb scattering centers inside the channel and reduces the carrier mobility and increased its resistance. Screw TDs played a much significant role than edge TDs in determining the reverse-bias leakage current of Schottky barrier diodes. Leakage current is affected slightly by the reduction of free carrier density in the channel for samples with a higher edge TD density, but screw TD, which acted as the current leakage path, was more deleterious to the reverse-bias leakage current of AlGaN/GaN structure.

Growth of GaN film on 150mm Si (111) using multilayer AlN∕AlGaN buffer by metal-organic vapor phase epitaxy method

High quality GaN film was successfully grown on 150mm Si (111) substrate by metal-organic vapor phase epitaxy method using AlN multilayer combined with graded AlGaN layer as buffer. The buffer layer structure, film quality, and film thickness are critical for the growth of the crack-free GaN film on Si (111) substrate. Using multilayer AlN films grown at different temperatures combined with graded Al1−xGaxN film as the buffer, the tensile stress on the buffer layer was reduced and the compressive stress on the GaN film was increased. As a result, high quality 0.5μm crack-free GaN epitaxial layer was successfully grown on 6in. Si substrate.

Effects of AlxGa1−xN interlayer for GaN epilayer grown on Si substrate by metal-organic chemical-vapor deposition

GaN film grown on Si substrate using multilayer AlN/AlxGa1−xN buffer is studied by the low-pressure metal-organic chemical-vapor deposition method. The AlxGa1−xN films with Al composition varying from 1 to 0.66 were used to accommodate the stress induced between GaN and the Si substrate during GaN growth. The correlation of the Al composition in the AlxGa1−xN films with respect to the stress induced in the GaN film grown was studied using high-resolution x-ray diffraction, including symmetrical and asymmetrical ω/2θ scans and reciprocal space maps. It is found that with proper design of the Al composition in the AlxGa1−xN buffer layer, crack-free GaN film can be successfully grown on 6 in. Si (111) substrates using multilayer AlN and AlxGa1−xN buffer layers.

Growth of High-Quality In0:4Ga0:6N Film on Si Substrate by Metal Organic Chemical Vapor Deposition

High-quality In0.4Ga0.6N film grown on GaN/AlN/Si(111) templates was obtained by metal organic chemical vapor deposition (MOCVD) with negligible phase separation. A template of high-quality GaN grown on a Si(111) substrate using AlN buffer layers was used for subsequent In0.4Ga0.6N growth. The GaN layer was 0.6 µm thick with rocking-curve full width at half maximum (FWHM) for a GaN(002) peak better than 430 arcsec. The In0.4Ga0.6N film grown was 0.3 µm thick with a dislocation density of 6×107 cm-2 and X-ray (ω–2θ) FWHM better than 130 arcsec.

Reactive Ion Etching of GaInP , GaAs , and AlGaAs

We have investigated the reactive ion etching of GaInP, GaAs, and AlGaAs. High etching selectivity of GaAs to AlGaAs (or to GaInP) can be achieved due to the formation of aluminum fluoride (AlF 3 ) and indium fluoride (InF 3 ) using a BCl 3 /SF 6 mixture. By using a CH 4 /H 2 mixture, a polymer film is accumulated on the GaAs surface after reactive ion etching. This polymer film inhibits the reactive ion etching of GaAs. There is no polymer film accumulated on the surface of GaInP. The polymer deposited on the surface of GaInP is removed as the etching products are being removed. Hence, a high etching selectivity of GaInP to GaAs can be achieved by using a CH 4 /H 2 mixture

The thermal stability of ohmic contact to n-type InGaAs layer

The thermal stability of ohmic contact to n-type InGaAs layer is investigated. When Ni/Ge/Au is used as the contact metal, the characteristics of the ohmic contact are degraded after thermal treatment. The specific contact resistance of (Ni/Ge/Au)-InGaAs ohmic contact after annealing at 450°C is about 15 times larger than that of as-deposited sample. This is due to the decomposition of InGaAs and the interdiffusion of Ga and Au. A new phase of Au4ln appears after annealing at 300°C. While in the case of Ti/Pt/Au, Au does not penetrate into the InGaAs layer as revealed by secondary ion mass spectroscopy. The specific contact resistance of (Ti/Pt/Au)-InGaAs ohmic contact after annealing at 450°C is eight times larger than that of as-deposited sample. Therefore, the thermal stability of (Ti/Pt/Au)-InGaAs ohmic contact is better than that of (Ni/Ge/Au)InGaAs ohmic contact.

In0.49Ga0.51P/GaAs heterostructures grown by low-pressure metalorganic chemical vapor deposition

We have successfully grown In0.49Ga0.51P/GaAs heterostructures and made InGaP‐based high electron mobility transistors (HEMTs) by low‐pressure metalorganic chemical vapor deposition. We have found the epitaxial layer of InGaP with a Hall mobility of 4073 cm2/V s (300 K) and the photoluminescence full width at half‐maximum of 1 meV (4.2 K) for GaAs, 12 meV (4.2 K) for In0.49Ga0.51P. Zinc‐induced disordering phenomenon was examined by transmission electron microscope. By Shubnikov‐de Haas measurement, we demonstrated the existence of a two‐dimensional electron gas in InGaP/GaAs heterojunctions. The sheet carrier concentration of 2DEG is around 8.8×1011 cm−2 at 1.5 K. A HEMT device with 1 μm×40 μm gate (pattern) shows an extrinsic transconductance of 65.5 mS/mm and an intrinsic transconductance of 266 mS/mm at 300 K.

Effect of Multiple AlN Layers on Quality of GaN Films Grown on Si Substrates

AbstractIn this paper, we present the effect of multiple thin high-low-high-temperature AlN (HLHT AlN) nucleation layers on GaN film quality. A 1.9-μm-thick GaN film grown on Si (111) substrate shows that the multiple HLHT AlN nucleation layers have a significant effect on GaN film quality. This process also plays a very important role in the growth of GaN films on Si (111) substrates. A high quality GaN film with a uniformly faceted surface with very low dislocation densities is obtained at the optimized multiple HLHT AlN nucleation layers 50-nm thick at a temperature of 1010-800-1010°C and a growth pressure of 50 Torr.

The effect of CdS QDs structure on the InGaP/GaAs/Ge triple junction solar cell efficiency

This work describes optical and electrical characteristics of InGaP/GaAs/Ge triple-junction (T-J) solar cells with CdS quantum dots (QDs) fabricated by a novel chemical solution. With the anti-reflective feature at long wavelength and down-conversion at UV regime, the CdS quantum dot effectively enhance the overall power conversion efficiency more than that of a traditional GaAs-based device. Experimental results indicate that CdS quantum dot can enhance the short-circuit current by 0.33 mA/cm2, which is observed for the triple-junction solar cells with CdS QDs of about 3.5 nm in diameter. Moreover, the solar cell conversion efficiency is improved from 28.3% to 29.0% under one-sun AM 1.5 global illumination I–V measurement.

A pseudomorphic GaInP/InP MESFET with improved device performance

A high-bandgap GaInP epitaxial material grown on InP to increase the Schottky barrier height of the InP MESFET is discussed. The Schottky gate materials used in this study were Au and Pt/sub 2/Si. The pseudomorphic GaInP/InP MESFET with an Au gate has a Schottky barrier height of 0.54 eV, and the reverse leakage current of the device is 10/sup -2/ times lower than that of the conventional InP MESFET. The extrinsic and intrinsic transconductance of the pseudomorphic MESFET are 66.7 and 104.2 mS/mm respectively for the 5- mu m-gate-length GaInP/InP MESFET. >