Y. H. Wang

Drastic reduction of series resistance in doped semiconductor distributed Bragg reflectors for surface‐emitting lasers

Modifications to reduce the series resistance in p‐type semiconductor distributed Bragg reflectors (DBR) consisting of ten pairs of quarter‐wavelength GaAs (high refractive index)/Al0.7Ga0.3As (low index) layers were made by inserting an intermediate Al0.35Ga0.65As layer or a 200 A superlattice of GaAs(10 A)/Al0.7Ga0.3As (10 A) at the GaAs/Al0.7Ga0.3As heterointerfaces. The specific DBR series resistance was reduced by two orders of magnitude to about 6.2×10−5 Ω cm2. These modifications did not alter the optical reflectivity and nearly identical reflection spectra were measured.

Structural and electrical characteristics of atomic layer deposited high κ HfO2 on GaN

High κ HfO2 was deposited on n-type GaN (0001) using atomic layer deposition with Hf(NCH3C2H5)4 and H2O as the precursors. Excellent electrical properties of TiN∕HfO2∕GaN metal-oxide-semiconductor diode with the oxide thickness of 8.8nm were obtained, in terms of low electrical leakage current density (∼10−6A∕cm2 at VFB+1V), well behaved capacitance-voltage (C-V) curves having a low interfacial density of states of 2×1011cm−2eV−1 at the midgap, and a high dielectric constant of 16.5. C-V curves with clear accumulation and depletion behaviors were shown, along with negligible frequency dispersion and hysteresis with sweeping biasing voltages. The structural properties studied by high-resolution transmission electron microscopy and x-ray reflectivity show an atomically smooth oxide/GaN interface, with an interfacial layer of GaON ∼1.8nm thick, as probed using x-ray photoelectron spectroscopy.

IMPROVED FORMATION OF SILICON DIOXIDE FILMS IN LIQUID PHASE DEPOSITION

This work is to reveal the novel technique of liquid phase deposition silicon dioxide (SiO2) films which will increase the deposition rate and also improve the film quality. It is well known that deposition at a lower temperature without residual OH− on the substrate is difficult to achieve. Therefore, it is important to treat the substrate wafer before deposition. The substrate surface dipped into hydrofluoric acid (HF) is usually terminated with hydrogen (H) and has hydrides (Si–H) which react with water so that hydroxyls (Si–OH) can be obtained. No silicon dioxide can be grown on a clean Si substrate without native oxide. Therefore, a model is proposed to show that native oxide growth with chemical pretreatment of HF and ultrapure deionized water has rich hydroxyl (OH) molecules on surface in order to grow silicon dioxide. Another constant parameter, the growth rate of SiO2 is found to increase linearly with the time of reaction with ultrapure deionized water. At the same concentration of boric acid an...

Extremely low temperature formation of silicon dioxide on gallium arsenide

This article demonstrates the growth of silicon dioxide (SiO2) on a gallium arsenide (GaAs) substrate by use of the liquid phase deposition (LPD) method at extremely low temperature (∼40 °C). This method cannot only grow SiO2 but it can also obtain good quality and reliability due to the suppression of interdiffusion in such a low temperature process. The deposition rate of LPD-SiO2 on GaAs is up to 1265 A/h. The refractive index of the LPD-SiO2 film on GaAs is about 1.42 with growth at 40 °C. When the LPD-SiO2 film on the GaAs substrate is used to fabricate a metal–oxide–semiconductor capacitor with a device area of 0.3 cm2, the surface charge density (Qss/q) is about 3.7×1011 cm−2 and the leakage current is 43.3 pA at −5 V. A proposed mechanism for the LPD of SiO2 on GaAs is also presented.

Surface morphologies of GaAs layers grown by arsenic‐pressure‐controlled molecular beam epitaxy

Surface morphologies of the molecular beam epitaxy (MBE)‐grown GaAs layers using background arsenic‐pressure‐control method were investigated. The growth parameters, such as substrate temperatures, growth rates, epilayer thicknesses, As/Ga ratios, doping concentrations, substrate types, etc., are related to the observed oval defect density. Protrusions and Ga‐droplet induced oval defects were formed during growth. The origin of the oval defects in our system is found to be the gallium oxide, not Ga ‘‘splitting’’ from the effusion cell. Surface preparations are also another important factor in reducing the oval defect density. Special triangular pyramidal defects with concave or acute top surfaces were found. They have the same major axis as oval defects. Also found were defects with perpendicular orientation to the oval defects. Such defects are attributed to contaminations on the surface and can be eliminated.

Effect of a chemical modification on growth silicon dioxide films on gallium arsenide prepared by the liquid phase deposition method

This article presents a chemical modification process to grow silicon dioxide (SiO2) on a gallium arsenide (GaAs) substrate using liquid phase deposition (LPD) at extremely low temperature (∼40 °C). In this process, pretreatment of the wafer by ammonia solution with buffer kept at pH=11–12 enriches OH radical formation on the GaAs surface, enhancing SiO2 deposition, providing good film quality, and reliability. The LPD SiO2 deposition rate on GaAs substrate is up to 1303 A/h. The refractive index of the LPD SiO2 film on GaAs substrate is about 1.423 with growth at 40 °C. When the LPD SiO2 film on GaAs substrate is used to fabricate a metal–oxide–semiconductor capacitor, the surface charge density (Qss/q) is about 3.7×1011 cm−2 and the leakage current is 43.3 pA at −5 V. A mechanism for the deposition of silicon dioxide on a GaAs substrate is proposed.

Normal incidence intersubband optical transition in GaSb/InAs superlattices

A novel intersubband optical transition, incorporating interband and p‐type intersubband optical transition mechanisms, in a suitably designed GaSb/InAs superlattice is proposed. Such a structure utilizes the strong mixing of GaSb light‐hole band with InAs conduction band and the heavy‐hole to light‐hole intervalence‐subband transition in the GaSb/InAs superlattice to obtain a strong normal incidence photoabsorption coefficient (over 8.0×104 cm−1) at a wavelength near 10 μm.

Improvement of peak‐to‐valley ratio by the incorporation of the InAs layer into the GaSb/AlSb/GaSb/AlSb/InAs double barrier resonant interband tunneling structure

InAs blocking layer is incorporated into the GaSb/AlSb/GaSb/AlSb/InAs double barrier resonant interband tunneling structure to improve the peak‐to‐valley ratios. It is found the ratio rises to 21 at room temperature and the peak current density keeps nearly constant for InAs layer reaches 30 A and then both of them decreases with the increase of InAs thickness. However, while the InAs blocking layer further increases to 240 A, the I‐V characteristic shows multiple negative differential resistance behavior. These interesting phenomena can be modeled to be due to the coupling effect of InAs blocking layer and GaSb well layer.

Observation of reduced current thresholds in GaAs/AlGaAs vertical‐cavity surface‐emitting lasers grown on 4° off‐orientation (001) GaAs substrates

GaAs/AlGaAs vertical‐cavity surface‐emitting lasers (VCSELs) with two semiconductor distributed Bragg reflectors (DBRs) were grown by molecular beam epitaxy. The threshold current was found to be 20–50% less on an average for VCSELs grown on the 4° off‐orientation (001) substrates than those on the on‐orientation ones. The lower threshold current was attributed to the smoother interfaces of the Al0.1Ga0.9As/AlAs DBRs in the off‐orientation growth observed by transmission electron microscopy. A threshold current and current density of 12 mA and 10.5 kA/cm2 were measured with an emission efficiency of 0.2 mW/mA.

MBE grown n + -i-δ(p + )-i-n + GaAs V-groove barrier transistor

The three-terminal n⁺-i-δ(p⁺)-i-n⁺V-groove barrier transistor (VBT) has been successfully fabricated by molecular beam epitaxy (MBE). The base terminal is connected to the δ(p⁺), the thin p⁺layer, by depositing aluminum on the etched V-groove. The demonstrated device possesses high potential of ultra-high-frequency (<tex>f_{r} > 30</tex>-GHz), high-power, and low-noise capability due to carriers transporting by thermionic emission and being controlled by the base-emitter bias.