J. C. P. Chang

The role of point defects and arsenic precipitates in carrier trapping and recombination in low‐temperature grown GaAs

GaAs epilayers were grown with a wide range of excess arsenic concentrations and subjected to various anneals to study the role of the point defects and arsenic precipitates in carrier trapping and recombination. Prior to anneal, the point defects rapidly trap photogenerated electrons and holes—usually on subpicosecond time scales. However, full electron‐hole recombination occurs on a significantly longer time scale. After anneal, the full electron‐hole recombination lifetime appears to be greatly reduced, indicating that the arsenic precipitates play a significant role.

Molecular Beam Epitaxy of Nonstoichiometric Semiconductors and Multiphase Material Systems

Abstract When arsenides are grown by molecular beam epitaxy at low substrate temperatures, as much as 2% excess arsenic can be incorporated into the epilayer. This excess arsenic is in the form of antisites, but there is also a substantial concentration of gallium vacancies. With anneal, there is a significant decrease in the arsenic antisite and gallium vancancy concentrations as the excess arsenic precipitates. With further anneal, the arsenic precipitates coarsen. This combination of low substrate temperature molecular beam epitaxy and a subsequent anneal results in a broad spectrum of materials, from highly defected epilayers to a two-phase system of semimetallic arsenic precipitates in an arsenide semiconductor matrix. These materials exhibit some very interesting and useful electrical and optical properties.

Incoherent interface of InAs grown directly on GaP(001)

We report molecular beam epitaxial growth of InAs on GaP(001), which has the largest lattice mismatch (11%) among all the arsenides and phosphides. Reflection high‐energy electron diffraction and high‐resolution transmission electron microscopy were used to optimize the growth and characterize the epilayer. It is found that the growth mode can be controlled by the surface V/III ratio: three‐dimensional and two‐dimensional layer‐by‐layer growths under As‐stable and In‐stable conditions, respectively. In both cases, a regular network of pure edge‐type (90°) misfit dislocations with a spacing of 4 nm was formed directly at the heterointerface, which corresponds to 85% of degree of strain relaxation. The epilayers grown under In‐stable conditions have relatively smooth surfaces with low threading dislocation densities. This is owing to the fact that the interface misfit dislocations were exclusively of the edge‐type which have no threading component and which relieve strain most effectively. The results demon...

THE ROLE OF EXCESS ARSENIC IN INTERFACE MIXING IN LOW-TEMPERATURE-GROWN ALAS/GAAS SUPERLATTICES

Undoped low‐temperature‐grown AlAs/GaAs superlattices experience pronounced interface intermixing with increasing anneal temperatures up to 900 °C. Quantum confinement shifts caused by intermixing of low‐temperature‐grown and standard‐temperature‐grown superlattices were studied using electromodulation spectroscopy. The effective activation energy for intermixing in the low‐temperature‐grown superlattices during 30 s isochronal postgrowth anneals was found to be (0.32±0.04) eV, anomalously smaller than for standard‐temperature‐grown superlattices. Roughening of the interfaces caused by arsenic precipitates accompanies the intermixing. Qualitative features of the intermixing have been confirmed using high resolution transmission electron microscopy and studies on x‐ray rocking curves.

Precipitation in Fe‐ or Ni‐implanted and annealed GaAs

We report the formation of metal/semiconductor composites by ion implantation of Fe and Ni into GaAs and a subsequent anneal to nucleate clusters. Electron diffraction experiments and high resolution transmission electron microscopy images indicate that these precipitates are probably hexagonal and metallic Fe3GaAs or Ni3GaAs with orientation relationship to GaAs of (1010)pp∥(422)m, (0002)pp∥(111)m, and [1210]pp∥[011]m. Correlation of the electrical and structural properties of the samples annealed at different temperatures shows that the buried Schottky‐barrier model has general applicability.

Magnetic and magnetoresistance measurements on iron-based nanoclusters in In0.53Ga0.47As

We have obtained magnetoresistance data on low iron-concentration samples (∼1%) showing a large negative magnetoresistance (3.2% at 5 K in 0.5 T) attributed to imbedded superparamagnetic clusters in In0.53Ga0.47As. The samples were prepared by ion implanting a p-In0.53Ga0.47As layer with iron followed by a rapid thermal anneal. Magnetic measurements confirm the formation of a cluster size distribution with a mean diameter of 6.2 nm and effective moment of 7000 bohr magnetons. The magnetization of these single domain ferromagnets is 50% saturated in a field of only 0.2 T even at room temperature which is important for device applications.

OPTICAL ABSORPTION BY AG PRECIPITATES IN ALGAAS

Optical absorption by silver nanoclusters in a dilute metal-semiconductor composite is calculated including the effects of size and shape on the surface plasmon absorption. Strong broadening of the Frohlich resonance peaks is caused by relatively minor shape variations. Optical transmission experiments and transmission electron microscopy experiments were performed on a Ag–Al0.3Ga0.7As composite formed by ion implantation followed by anneal. Silver precipitates are present in a clearly defined implant layer. A broad featureless optical absorption is observed that extends below the band gap, and which increases approximately linearly with Ag-ion dose.

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.

ELECTRICAL AND STRUCTURAL PROPERTIES OF BE- AND SI-DOPED LOW-TEMPERATURE-GROWN GAAS

Excess As is incorporated in GaAs grown at low substrate temperatures by molecular beam epitaxy. Excess As is distributed in the epilayer as defects and the material exhibits considerable strain. When annealed to moderate temperatures, the strain is seen to disappear and the excess As is now in the form of semimetallic clusters. It has been proposed that these As clusters form buried Schottky barriers with the GaAs matrix and are surrounded by spherical depletion regions. In this article, we examine the effects of doping on the material properties and compare our results to the buried Schottky barrier mode. Si‐doped GaAs epilayers grown at 250 °C, with doping densities between 5×1017 and 5×1018 cm−3, were annealed to temperatures between 700 and 1000 °C for 30 s. Be‐doped GaAs epilayers grown at 250 °C, with doping densities between 5×1017 and 5×1019 cm−3, were annealed to temperatures between 700 and 900 °C for 30 s. Using extensive Hall measurements and transmission electron microscopy, we observe that ...