J.-W. Pan

Material properties of compositional graded InxGa1−xAs and InxAl1−xAs epilayers grown on GaAs substrates

The residual strain, crystallographic tilt, and surface topography of InxGa1−xAs and InxAl1−xAs (0<x<0.3) epilayers grown on GaAs substrates are investigated. The residual strain of the InxAl1−xAs grown on graded InyAl1−yAs is shown to be strongly dependent on the thickness of the underlying‐graded buffer layers and is larger than that of the InGaAs of the same structure. The crystallographic tilt of the InGaAs epilayers with respect to GaAs substrate is found to be strongly dependent on the growth temperature as well as the layer structure of the underlying buffer layer, while that of InAlAs is insensitive to these two factors. This behavior is attributed to the different roughness of the growth front between these two material systems and is consistent with the observation by atomic force microscopy.

HYDROGENATED AMORPHOUS-SILICON CARBIDE P-I-N THIN-FILM LIGHT-EMITTING-DIODES WITH BARRIER LAYERS INSERTED AT P-I INTERFACE

To improve the electroluminescence (EL) intensity of the hydrogenated amorphous silicon carbide (a-SiC:H) pi-n thin-film light-emitting diode (TFLED), a barrier-layer (BL) structure had been inserted at its p-i interface and used to enhance the hole injection efficiency of TFLED under forward-bias operation. Two TFLEDs with different BL structures were studied. The device 1 had a 25 A i-type single-barrier structure and the device II had an i-type double-barrier structure of barrier(10 A)/well(10 A)/barrier(10 A). The obtainable brightness of device I was 342 cd/m 2 at an injection current density of 600 mA/cm 2 . On the other hand, the device II had a brightness of 256 cd/m 2 at 800 mA/cm 2 . These brightnesses were about 3 orders of magnitude higher than that of a basic a-SiC:H p-i-n TFLED

Electroluminescence characteristics and current-conduction mechanism of a-SiC:H p-i-n thin-film light-emitting diodes with barrier layer inserted at p-i interface

In order to improve the electroluminescence (EL) characteristics of the hydrogenated amorphous silicon carbide (a-SiC:H) p-i-n thin-film light-emitting diode (TFLED), a barrier layer (BL) was inserted at its p-i interface to enhance the hole injection efficiency under forward-bias operation. The a-SiC:H TFLEDs with various optical gaps of BL had been fabricated and characterized. In addition, a composition-graded n/sup +/-layer was used to reduce its series and contact resistances to the Al electrode and hence the EL threshold voltage (V/sub th/) of an a-SiC:H BL TFLED. The highest obtainable brightness of an a-SiC:H BL TFLED was 342 cd/m/sup 2/ at an injection current density of 600 mA/cm/sup 2/ and the lowest EL V/sub th/ achievable was 6.0 V. The current-conduction mechanism of an a-SiC:H BL TFLED had also been investigated. Within the lower applied-bias region, it showed an ohmic current, while within the higher applied-bias region, a space-charge-limited current (SCLC) was observed. >

Study of the optical properties of In0.52(AlxGa1−x)0.48As by variable angle spectroscopic ellipsometry

The optical properties of In0.52(AlxGa1−x)0.48As epilayers with various x values were systematically studied using variable angle spectroscopic ellipsometry in the wavelength range of 310–1700 nm. The refractive indexes were determined and could be given as n(x)=0.12x2–0.51x+3.6 at the wavelength of 1.55 μm. The measured thickness of the epilayers agrees within 5.2% of the nominal thickness. The energies and broadening parameters of the E1 and E1+Δ1 transitions as a function of Al composition were also examined based on the second‐derivative spectra of the dielectric function. The comparison between the results and the reported data is presented.

Schottky barrier heights of InxAl1−xAs (0≤x≤0.35) epilayers on GaAs

The electrical characteristics of Al Schottky diodes on n‐type InxAl1−xAs (0≤x≤0.35) were investigated in detail by current‐voltage and capacitance‐voltage measurements. These high‐quality InAlAs epilayers were grown on GaAs using step‐graded buffers under proper growth conditions. It was found that the Schottky barrier height of the epilayers increases with Al content as opposed to what was predicted previously. The effect of the interfacial oxide layer on the determination of Schottky barrier height is also presented.

The study of the optical properties of In/sub 0.52/(Al/sub x/Ga/sub 1-x/)/sub 0.48/As by variable angle spectroscopic ellipsometry

The optical properties of In/sub 0.52/(Al/sub x/Ga/sub 1-x/)/sub 0.48/As epilayers with various x values were systematically studied using variable angle spectroscopic ellipsometry in the wavelength range of 310-1700 nm. The refractive indexes were determined. The energies and broadening parameters of the E/sub 1/ and E/sub 1/+/spl Delta//sub 1/ transitions as a function of Al composition were also examined based on the second-derivative spectra of the dielectric function. The comparison between our results and the reported data is presented.

Fully quaternary In/sub 0.52/(Al/sub 1-x/Ga/sub x/)/sub 0.48/As/In/sub 0.53/(Al/sub x/Ga/sub 1-x/)/sub 0.47/As (x=0.1, 0.2) heterostructures on InP for HFETs

A fully quaternary (FQ-) In/sub 0.52/(Al/sub 1-x/Ga/sub x/)/sub 0.48/As/In/sub 0.53/(Al/sub x/Ga/sub 1-x/)/sub 0.47/As (x=0.1, 0.2) heterostructure was introduced into doped-channel FETs (FQ-DCFETs) on InP substrates. Based on our previous studies, we observed that by adding a small amount of Ga (10%) atoms into the InAlAs Schottky and buffer layers in the HEMT structure, device performance can be enhanced due to a better quality of InAlGaAs material. Furthermore, by adding a small amount of Al (10% or 20%) atoms into the InGaAs channel layers, the associated impact ionization process can be suppressed in this InAlGaAs channel, resulting in an enhancement of breakdown voltage. Therefore, in this report, we combined both techniques to realize the fully quaternary HFETs and characterize their performance.