T. P. Chin

Determination of V/III ratios on phosphide surfaces during gas source molecular beam epitaxy

Phosphorus‐controlled growth rate of homoepitaxial (100) InP, GaP, and AlP on GaP substrates by gas source molecular beam epitaxy was investigated. Elemental group‐III sources and thermally cracked phosphine were used. The growth rate was monitored by the specular beam intensity oscillations of reflection high‐energy electron diffraction. This technique gives exact values of V/III ratio on the surface by measuring the amount of phosphorus which is actually incorporated into the film. Here the V/III ratio is defined as P‐controlled growth rate divided by group‐III‐controlled growth rate instead of the beam flux V/III ratio. Also the phosphorus surface desorption activation energies were measured to be 0.61 eV and in the range between 0.89 and 0.97 eV for InP and GaP, respectively.

In situ determination of phosphorus composition in GaAs1−xPx grown by gas‐source molecular beam epitaxy

We report for the first time an in situ determination of phosphorus compositions in a mixed group‐V compound, such as GaAs1−xPx, grown by gas‐source molecular beam epitaxy. Reflection high‐energy electron diffraction intensity oscillations from As‐limited and (As+P)‐limited growth are observed on a Ga‐rich GaAs surface. The phosphorus composition is therefore deduced from the different growth rates. Viability of this technique is strongly confirmed by the good agreement with the phosphorus compositions determined ex situ by x‐ray rocking curve measurements on GaAs/GaAsP strained‐layer superlattice structures.

Impact ionization coefficients in (100) GaInP

Electron and hole impact ionization coefficients in (100)Ga0.5In0.5P have been measured by photomultiplication measurements. The ratio of hole to electron ionization coefficients, β/α, is shown to decrease from 2 to 1 when the electric field is increased from 3.5×105 to 6.5×105 V/cm. As confirmation, breakdown voltages were measured for several p+−n−−n+ diodes with various concentrations in the n− region. The values observed showed good agreement with those calculated from the ionization coefficients. Typical breakdown voltages are on the order of 1.6 times higher than those expected for GaAs.

Gas‐source molecular beam epitaxial growth, characterization, and light‐emitting diode application of InxGa1−xP on GaP(100)

Highly lattice‐mismatched InxGa1−xP (x≤0.38) layers were grown on GaP substrates by gas‐source molecular beam epitaxy. A relatively thin, compositionally linear‐graded buffer layer was used to reduce the number of threading dislocations. Studies by double‐crystal x‐ray diffraction and transmission electron microscopy show this buffer layer to be 97% strain‐relaxed along both 〈110〉 directions with dislocations well confined within the graded buffer and the substrate. Threading dislocation densities in the top layers were less than 1×107 cm−2. Room‐temperature photoluminescence, ranging from 560 to 600 nm, is achieved. Heterojunction p‐i‐n diodes emitting at 560 nm at 300 K exhibit good rectifying and reverse breakdown characteristics.

Multiple dislocation loops in linearly graded InxGa1−xAs (0≤x≤0.53) on GaAs and InxGa1−xP (0≤x≤0.32) on GaP

We report transmission electron microscopy studies of dislocation structures in two lattice‐mismatched III‐V systems, InxGa1−xAs (0≤x≤0.53)/GaAs and InxGa1−xP (0≤x≤0.32)/GaP, grown by gas‐source molecular beam epitaxy. Multiple dislocation‐loops, extending from within a linearly graded buffer layer to deep inside the substrate, were observed in both systems. All dislocations in each set of loops consisted of 60° dislocations with the same Burgers vector on a similar {111} glide plane. The density in the graded buffer and the substrate was estimated to be 2×109/cm2, and their appearance was associated with low threading dislocation densities and good optical quality in material grown on top of the buffer layer, InP/In0.53Ga0.47As on GaAs or In0.32Ga0.68P on GaP.

Nature of band bending at semiconductor surfaces by contactless electroreflectance

The nature of the band bending at semiconductor surfaces (and related carrier type) is an important materials parameter. We demonstrate that an electroreflectance mode which employs a capacitorlike configuration can conveniently be used for this evaluation in a contactless manner. Results will be presented on n‐ and p‐type bulk GaAs, semi‐insulating GaAs, nominally undoped In0.15Ga0.85As and n‐ and p‐type GaAs and InP structures with large, almost uniform electric fields.

Heavily carbon-doped p-type GaAs and In0.53Ga0.47As grown by gas-source molecular beam epitaxy using carbon tetrabromide

Highly p-type carbon-doped GaAs and In 0.53 Ga 047 As grown by gas-source molecular beam epitaxy were obtained by using carbon tetrabromide as the carbon source. In the low 10 19 cm -3 range almost all carbon atoms are electrically active in GaAs, and at least 85% of the carbon atoms are activated at a concentration as high as 1.2×10 20 cm -3 . A hole concentration of 9×10 19 cm -3 in In 0.53 Ga 0.47 As, among the highest reported to date, was achieved. No hydrogenation problem was observed

InGaAs/InP and InAsP/InP quantum well structures on GaAs (100) with a linearly graded InGaP buffer layer grown by gas‐source molecular beam epitaxy

A linearly graded InxGa1−xP (x=0.48–1) buffer layer is used for growing a high‐quality InP layer on a GaAs substrate. We show that an InxGa1−xP buffer layer is superior to an InyGa1−yAs buffer layer because it is transparent to long wavelengths and allows a less stringent composition control. InGaAs/InP single quantum wells and InAsP/InP multiple quantum wells grown on the InP/InxGa1−xP/GaAs substrate show comparable quality to similar structures grown on InP (100) substrates. Photocurrent spectra for the latter exhibit quantum‐confined Stark effect near 1.3 μm.

Operation and device applications of a valved‐phosphorus cracker in solid‐source molecular‐beam epitaxy

Solid phosphorus is successfully incorporated into a molecular‐beam epitaxy system by a valved‐cracker for the growth of phosphorus‐based materials. The operating parameters are established through beam flux and reflection high‐energy electron diffraction measurements. InP and InGaP lattice matched to GaAs were grown and characterized by Hall measurements, photoluminescence, electroreflectance, x‐ray diffraction, and transmission electron microscopy. The first microwave performance (ft=44 GHz, fmax=65 GHz) of an InGaP/GaAs heterojunction bipolar transistor grown by solid‐phosphorus source is reported.

High‐resolution x‐ray diffraction of InAlAs/InP superlattices grown by gas source molecular beam epitaxy

Structural properties of InAlAs/InP superlattices grown by gas source molecular beam epitaxy on (001)InP were investigated extensively with high‐resolution x‐ray diffraction. Very high quality material was obtained as indicated by narrow peak widths, numerous satellite peaks, and distinct Pendellosung fringes. Intermixing of group‐V elements at each interface was quantified by dynamical simulations of (004), (002), and (115) reflections. The accuracy of the fits to both peak positions and peak intensities for all three reflections provides strong evidence for the proposed four‐layer periodic structure.