C. R. Wie

Use of a valved, solid phosphorus source for the growth of Ga0.5In0.5P and Al0.5In0.5P by molecular beam epitaxy

We report on a new method for the generation of phosphorus beams in molecular beam epitaxy: the use of a valved, solid cracker source. The valved solid source avoids previous difficulties associated with the use of solid phosphorus, and provides an attractive alternative to the use of phosphine. The use of red phosphorus does not interfere with the subsequent growth of high quality arsenides in the same growth chamber. The performance of this valved phosphorus source is illustrated by the growth of two ternary phosphides, Ga0.5In0.5P and Al0.5In0.5P. The quality of the phosphides reported here is comparable to the best results reported by other growth techniques. The effects of composition, growth temperature, and P2 flux on the films’ characteristics are reported. Indium desorption during growth is found to be substantially greater in AlInP than in GaInP.

Relaxation and rocking-curve broadening of strained (Ga, In)As single layers on (001) GaAs

We have measured the lattice relaxation of various strained Ga1−xInxAs layers which are thicker than the equilibrium critical thickness. Samples with a thickness near the energy balance model critical thickness exhibited a large relaxation. We have analyzed the strain relaxation data in a GaInAs/GaAs system using the Dodson–Tsao plastic flow model [Appl. Phys. Lett. 52, 852 (1988)]. It was found that the model provides a reasonably good fit to the data, however, the model parameters have widely different values for the GaInAs/GaAs samples with different mismatches. One parameter of the model shows an approximate inverse‐square‐law dependence on the misfit. The rocking‐curve linewidths are presented for the GaInAs layers. The measured linewidths are discussed in terms of the theoretical linewidth, dynamical x‐ray diffraction, and defect density depth distribution.

Characterization of metamorphic InxAl1−xAs∕GaAs buffer layers using reciprocal space mapping

The depth profiles of metamorphic InxAl1−xAs (0.05<x<1) buffer layers grown on GaAs substrates were characterized using the x-ray reciprocal space mapping. Three types of metamorphic samples were investigated and compared: step grade, single-slope linear grade, and dual-slope linear grade. The lattice mismatch, residual strain, crystallographic tilt, tilt azimuth, and the full width at half maximum were obtained from the reciprocal space maps. The tilt angle of linearly graded buffer layers stayed low at low In compositions until In≈60%, at which composition the tilt angle increased abruptly. All linear-grade samples had an untilted relaxed structure in the low In region (below 60% In) and a tilted structure in the upper, high In region (above 60% In). The average lattice mismatch between the untilted relaxed structure and the tilted structure determines the tilt angle. The tilt angle of the step-graded layers increased at a near-linear rate as the In composition was increased. The tilt azimuth was interm...

Rocking curve peak shift in thin semiconductor layers

A simple x‐ray diffraction method for determining layer composition and mismatch is by measurement of the separation of peaks in a rocking curve. This method can only be used for layers with a thickness above a certain value. This minimum thickness can be significantly large for layers with a small lattice mismatch as in AlGaAs/GaAs or isoelectronic‐doped III‐V semiconductor layers. We give such an example and show that the interference between the diffraction amplitudes of the thin layer and that of the substrate is responsible for the peak shifting of the layer Bragg peak. When this peak shifting is significant, the kinematical diffraction theory and the peak separation method should not be used for the mismatch measurement, and only the dynamical diffraction theory simulation should be used. We present a criterion on the layer thickness, below which the dynamical theory simulation must be used. This thickness is inversely proportional to the lattice mismatch and does not depend on the diffraction geometry, wavelength, and substrate material.

X-ray interference in quantum-well laser structures

X‐ray interference effects are observed in the simulated rocking curves of quantum‐well laser structures. It is shown that the interference effects appear in the cladding layer peak of rocking curves for a generic sample structure of a thin heterojunction layer of composition A cladded with two thicker layers of composition B. Depending on the detailed layer structure and the lattice mismatch, the sandwiched quantum‐well layer can be as thin as 2–3 A in order to affect the interference structure of the cladding layer peak. For a given mismatch, the interference effect occurs around a certain minimum thickness and similar interference structures appear periodically with increasing quantum‐well layer thickness. This effect can be used to estimate the quantum‐well layer thickness with a high accuracy. A simple model is used to calculate the thickness period as a function of lattice misfit and diffraction geometry. The calculation results explain the simulation results.

Deep level studies in MBE GaAs grown at low temperature

The photo-induced current transient spectroscopy (PICTS), thermoelectric effect spectroscopy (TEES) and thermally stimulated current (TSC) spectroscopy have been used to characterize the deep levels in the GaAs materials grown at low temperature by molecular beam epitaxy. At least five hole traps and five electron traps have been identified by the TEES measurement employing a simplified sample arrangement. We have studied the behavior of various traps as a function of the growth temperature and the post-growth annealing temperature. Some of the shallower hole traps were annealed out above 650‡ C. Electron traps atEc- 0.29 eV andEc- 0.49 eV were present in the material, and have been identified as M3 and M4, respectively. The dominant electron trap, atEc- 0.57 eV, is believed to be associated with the stoichiometric defect caused by the excess As in the material, and our data show evidence of forming a defect band by this trap. A possible model involving As precipitates is proposed for this trap atEc-0.57 eV.

A simple and reliable method of thermoelectic effect spectroscopy for semi-insulating III-V semiconductors

We have developed a simpler and more reliable method of thermoelectric effect spectroscopy (TEES), eliminating the second heater in the technique. We have applied this method to the deep level studies in the semi‐insulating undoped or Cr‐doped GaAs materials and in the GaAs epitaxial layers grown at a low temperature by molecular beam epitaxy. We have found that the electrical contacts made on front and back surfaces of the sample are more reliable for the TEES measurement than both contacts made on the same surface. In this contact arrangement, the temperature difference of about 1–2 K between the back and front surfaces is enough to produce a clear and reliable TEES data, without the need for a second heater. The results obtained by TEES are consistent with the results obtained by photoinduced transient spectroscopy (PITS) and by thermally stimulated current (TSC) measurements. The TEES results clearly distinguish between the electron traps and the hole traps. We discuss the results on the various semi‐...

Kinematical x-ray diffraction model with a new boundary condition for analysis of Bragg-peak profiles of layered crystals

A new boundary condition is employed in the kinematical model analysis of Bragg‐peak profiles of layered single crystals, which is the dynamical reflection amplitude of the substrate instead of the previously used dynamical intensity. It is shown that this boundary condition properly accounts for the angular shift effect in the Bragg‐peak profile of very thin epitaxial layers and superlattices. A kinematical model simulates properly the interference profiles in the C‐layer Bragg peak of C/A/C/sub‐type samples, but not in the B‐layer Bragg peak of the B/A/B‐type samples. The simulated and experimental rocking curves for the thin single‐layer AlGaAs/GaAs and GaInAs/InP samples and for an AlGaAs/GaAs superlattice sample are discussed. Rocking curves are simulated by using the dynamical diffraction theory and the kinematical model with the old or new boundary condition. A matrix method for the dynamical theory superlattice simulation is also presented. The superlattice simulation using this matrix method is f...

PHOSPHORUS-VACANCY-RELATED DEEP LEVELS IN GAINP LAYERS

Deep levels in lattice‐matched Ga0.51In0.49P/GaAs heterostructure have been investigated by thermal‐electric effect spectroscopy (TEES) and temperature‐dependent conductivity measurements. Four samples were grown by molecular‐beam epitaxy with various phosphorus (P2) beam‐equivalent pressures (BEP) of 0.125, 0.5, 2, and 4×10−4 Torr. A phosphorus vacancy (VP) ‐related deep level, an electron trap, was observed located at EC−0.28±0.02 eV. This trap dominated the conduction‐band conduction at T≳220 K and was responsible for the variable‐range hopping conduction when T<220 K. Its concentration decreased with the increasing phosphorous BEP. Successive rapid thermal annealing showed that its concentration increased with the increasing annealing temperature. Another electron trap at EC−0.51 eV was also observed only in samples with P2 BEP less than 2×10−4 Torr. Its capture cross section was 4.5×10−15 cm2. This trap is attributed to VP‐related complexes.

Increased peak current in AlAs/GaAs resonant tunneling structures with GaInAs emitter spacer

Self‐consistent simulation results are presented for the symmetric barrier AlAs/GaAs/AlAs resonant tunneling structures with a GaInAs emitter spacer well [Appl. Phys. Lett. 58, 1077 (1991)]. A simple model is used to handle the two‐dimensional emitter accumulation electrons. These accumulation electrons below the emitter launching energy are treated as pseudo three‐dimensional electrons, distributed continuously down to a certain minimum energy. With a proper choice of this bottom energy, a good agreement is achieved in the peak position between the simulation results and the experimental data. The best fit value of the bottom energy for the accumulated electrons was about 2/3ΔEc below the emitter conduction band edges for all diodes. Also, the simulation results could explain the systematic variation of the experimental peak current and voltage values as a function of the GaInAs spacer well depth. In order to provide a design guideline, the layer parameters were systematically varied and the simulation r...