Y. C. Chen

Molecular‐beam epitaxial growth of high‐quality InSb on InP and GaAs substrates

Epitaxial layers of InSb were grown on InP and GaAs substrates by molecular beam epitaxy. The dependence of the epilayer quality on flux ratio, J sub Sb4/J sub In, was studied. Deviation from an optimum value of J sub Sb4/J sub In (approx. 2) during growth led to deterioration in the surface morphology and the electrical and crystalline qualities of the films. Room temperature electron mobilities as high as 70,000 and 53,000 sq cm /V-s were measured in InSb layers grown on InP and GaAs substrates, respectively. Unlike the previous results, the conductivity in these films is n-type even at T = 13 K, and no degradation of the electron mobility due to the high density of dislocations was observed. The measured electron mobilities (and carrier concentrations) at 77 K in InSb layers grown on InP and GaAs substrates are 110,000 sq cm/V-s (3 x 10(15) cm(-3)) and 55,000 sq cm/V-s (4.95 x 10(15) cm(-3)), respectively, suggesting their application to electronic devices at cryogenic temperatures.

Determination of critical layer thickness and strain tensor in InxGa1−xAs/GaAs quantum‐well structures by x‐ray diffraction

We have used the double‐crystal x‐ray rocking curve technique to determine lattice constant, strain relaxation, thickness, and critical thickness of a thin InxGa1−xAs layer embedded in GaAs. In this work we have measured and analyzed x‐ray data over a wide scan angle (∼2.0°). This allows the simultaneous determination of buried layer thickness and strain. The measurement results were analyzed by the dynamical diffraction theory. The critical thickness for an InGaAs layer embedded in GaAs obtained from x‐ray data is shown to be larger than that predicted by the force balance model. The strain tensors as a function of layer thickness are also analyzed for the buried InxGa1−xAs of different x values.

The relation of the performance characteristics of pseudomorphic In0.53+xGa0.47−x As/In0.52Al0.48As (0≤x≤0.32) modulation‐doped field‐effect transistors to molecular‐beam epitaxial growth modes

We have examined the growth and device characteristics of In0.53+x Ga0.47−x As/ In0.52 Al0.48 As (0≤x≤0.27) pseudomorphic modulation‐doped field‐effect transistors on InP substrates. In situ reflection high energy electron diffraction oscillation studies were carried out to study the growth of pseudomorphic InGaAs on GaAs and InP substrates. The data from these measurements and a theoretical formalism based on energy minimization suggest that in the pseudomorphic growth regime increased strain causes growth modes to change from two‐dimensional layer‐by‐layer to a three‐dimensional island mode. The resulting interface roughness is used as a parameter to explain the observed trends in channel mobility and device performance. It is also shown that altered growth techniques, such as migration enhanced epitaxy, in which the surface reconstruction may be changed, can restore the layer‐by‐layer growth mode for large amounts of strain in the pseudomorphic layer.

Carrier capture and relaxation in narrow quantum wells

In separate confined heterostructure (SCH) lasers, injected electrons and holes thermalize into a quantum well after diffusion through the outer cladding layers. The carriers move towards equilibrium by emitting optical phonons. In narrow quantum wells, as compared to the 1-2 ps required in bulk semiconductors, this phonon emission process can be considerably slowed down due to the 2-D density of states and the nature of the electron-optical phonon interaction. This process has been studied theoretically using a Monte Carlo program which allows us to see the carrier distribution as a function of time. Typical times for carrier relaxation are 10-15 ps for a 50 /spl Aring/ GaAs well with Al/sub 0.30/Ga/sub 0.70/As barriers and /spl sim/5 pS for a 200 /spl Aring/ well. These calculations have been complemented by time-resolved photoluminescence measurements on SCH structures where the relaxation time from a 3D distribution into In/sub 0.20/Ga/sub 0.80/As/GaAs wells is measured at T=200 K. Carrier relaxation times of 50, 41, 22, and 17 ps are obtained for wells of sizes 30, 40, 50, and 100 /spl Aring/, respectively. The results show clearly that the use of narrow quantum wells in low threshold lasers will pose a serious limitation to the efficiency and small-signal modulation bandwidth of these devices. >

Suppression of defect propagation in semiconductors by pseudomorphic layers

The propagation of defects in semiconductor heterostructures has been studied both theoretically and experimentally. The simple model shows that defects originating from lattice‐matched regions can be prevented from entering, or can be trapped by, a pseudomorphic layer, depending on the signs of the strain induced by the defect and the strain in the pseudomorphic layer. A pseudomorphic layer can therefore prevent the defect from propagating across in and entering the critical active region of a device. Experimentally, the photoluminescence intensities of Al0.4Ga0.6As/GaAs quantum wells with and without pseudomorphic In0.2Ga0.8As layers for prevention of defect propagation have been compared. GaAs substrates of high etch pit density were used to generate defects below the quantum well and silicon implantation was used to generate defects above it. The elevated temperatures during molecular‐beam‐epitaxial growth and postimplant rapid thermal annealing serve to assist in defect propagation in the respective ...

Transport properties of InAsxSb1−x (0≤x≤0.55) on InP grown by molecular‐beam epitaxy

Molecular‐beam epitaxy has been successfully used to grow InAsxSb1−x on InP substrates with good electrical characteristics. The samples are all n type with electron concentrations varying in the range (3–9)×1015 cm−3. The mobilities are high (70 000 and 110 000 cm2/V s at 300 and 77 K, respectively) in InSb and the alloys. More importantly, the mobilities remain high at the low temperatures in the alloys also, without any type conversion. The mobility data have been analyzed taking into account the appropriate scattering mechanisms. The alloy scattering potential in InAs0.24 Sb0.76 is estimated to be 0.3 V.

Direct measurement of the Hall factor for holes in relaxed Si1−xGex (0<x<1)

The Hall factor for holes in relaxed p‐type Si1−xGex alloys has been determined from mobility measurements at magnetic fields up to 7 T at 290 K. Our data together with previously published values for Si and Ge suggest that r for holes in SiGe varies between 0.73 and 1.7 with a possible strong bowing.

High-performance monolithic pin-MODFET transimpedance photoreceiver

The performance characteristics of a transimpedance photoreceiver using a In/sub 0.53/Ga/sub 0.47/As p-i-n photodiode integrated with a 0.1- mu m-gate-length regrown pseudomorphic In/sub 0.60/Ga/sub 0.40/As MODFET grown by MBE have been investigated. The regrown MODFETs have extrinsic transconductance values as high as 610 mS/mm and channel currents up to 350 mA/mm at a drain bias of 1.5 V. The measured temporal response of the photoreceiver exhibits a FWHM value of 90 ps, which indicates a bandwidth of approximately 6 GHz and expected 10-Gb/s operation. The transimpedance gain was as high as 55 dB- Omega with an 800- Omega feedback resistor.<<ETX>>

Reduction of Be out‐diffusion from heavily doped GaAs:Be layers by pseudomorphic InxGa1−xAs barrier layers

The effectiveness of suppressing Be out‐diffusion from a Be‐doped GaAs layer by strained InGaAs layers using secondary ion mass spectroscopy has been evaluated. The experimental structures consist of an 800 A Be‐doped (∼1×1019 cm−3) GaAs layer sandwiched between 80 A InxGa1−xAs (x=0,0.1,0.25) layers. The samples were subjected to rapid thermal annealing (RTA) at 750 °C for 6 min. It is clearly observed that Be diffusion beyond the InGaAs layers is the fastest for the structure with x=0 and the slowest for the structure with x=0.25.

Impact ionization coefficients for electrons and holes in strained In0.2Ga0.8As and In0.15Ga0.63Al0.22As channels embedded in Al0.3Ga0.7As

We have measured impact ionization coefficients, α and β, in 150 A pseudomorphically strained materials for the first time. The measurements were made on specially designed lateral p‐i‐n diodes. α and β in lattice‐matched GaAs layers are found to be lower than those in strained In0.2Ga0.8As and higher than those in strained In0.15Ga0.63Al0.22As. β is larger than α in all the samples. The results are discussed in terms of the changes in the band structure due to biaxial strain.