P. A. Barnes

Raman scattering of InGaAs/InP grown by uniform radial flow epitaxy

Uniform radial flow epitaxy, a novel growth technique, has been used to grow InGaAs films on InP. Epitaxial layers above and below the critical thickness for the onset of slip were grown. We used Raman spectroscopy to characterize the quality of epitaxial layers, determine alloy composition, and measure the strain. Raman spectra from both pseudomorphic (strained) and relaxed (unstrained) InGaAs films were obtained at 300 and 80 K. The difference in the frequencies of their GaAs‐like longitudinal optical phonons was used to calculate stress for the strained InGaAs/InP, leading to a direct formula for the evaluation of the layer stress.

Oxidation Studies for 6H-SiC

Polytype 6H silicon carbide samples having polar faces terminated with either carbon (000(bar 1)) or silicon (0001) have been oxidized at 810°C for varying times using a microwave plasma source. Silicon dioxide layer thicknesses have been determined using Rutherford backscattering techniques, and the oxidized samples were further characterized using capacitance-voltage techniques and the methods of Raman spectroscopy. Results indicate that oxide layers of comparable quality to those produced using standard thermal oxidation methods can be obtained in less time at lower temperature.

Metallization Studies on Epitaxial 6H-SiC

A study of electrical and physical data for metals deposited on n and p—type epitaxial 6H—SiC is reported. The metals investigated were Ni, NiCr, W, TiW, and Al. Electrical characterization included IV and CV data for Schottky contacts and specific contact resistance for ohmic contacts. The surface preparation prior to metallization was found to be critical to the quality of the contacts formed. The near surface region of the metal—semiconductor interface was investigated using Rutherford Backscattering (RBS) and light ion channeling (LIC) to detect interdiffusion and lattice damage. The ion scattering experiments were complimented with Auger Electron Spectroscopy (AES) and X—ray Photoelectron Spectroscopy (XPS) measurements. Surface morphology was investigated using SEM analysis including Energy Dispersive X—ray (EDX) analysis.

Current–voltage characteristics of a GaAs Schottky diode accounting for leakage paths

Many fabricated Schottky diodes exhibit significant deviations from the theoretically calculated current–voltage (I–V) characteristics of ideal Schottky diodes. Attempts have been made to account for this deviation using interface states or surface state densities. Previous models have used the interfacial layer model to analyze the nonideal I–V characteristics of a GaAs Schottky barrier. We show here how nonideal behavior can be explained by considering surface leakage currents and material resistance. The standard figure of merit of Schottky diodes is the ideality factor, which can be obtained from measurements of δV/δu200aln(I). By taking into account device resistance and shunt leakage paths with physically appropriate parameters, a relationship between δV/δu200aln(I) and voltage can be established, which yields a better understanding of transport across the interface(s) of real Schottky diodes.

Thermal and electric field induced defects in InP metal‐insulator‐semiconductor structures

The presence of deep levels in several samples of InP metal‐insulator‐semiconductor (MIS) structures was studied using the deep level transient spectroscopy technique. The InP MIS structures were fabricated using three different methods of oxide formation, two of which are chemical oxides and the third is plasma‐grown oxide. Defect levels ranging from (Ec−0.22) to (Ec−0.6) eV were observed in the samples. However, the levels at about (Ec−0.22) and (Ec−0.35) eV were detected only after increasing the reverse‐bias voltage to −2 V at a temperature of about 390 K. This phenomenon occurred in all the samples studied, irrespective of the method of oxidation. The appearance of the peaks corresponding to the shallower traps is irreversible and may explain the performance instability commonly encountered in InP MIS‐based devices.

Lateral overgrowth and epitaxial lift-off of InP by halide vapor-phase epitaxy

The orientation dependence of lateral overgrowth and vertical growth of InP deposits selectively grown through stripe openings in a phosphosilicate glass mask was investigated using halide vapor-phase epitaxy. The lateral overgrowth was observed to be strongly dependent on the orientation of stripe openings, and the vertical growth was shown to be inversely correlated to the lateral overgrowth. For a sufficiently long growth time, the growth fronts of lateral overgrowth layers from adjacent stripe openings merged together to form a completely overgrown layer. The morphology of the region where the growth fronts are merged was shown to be dependent on the orientation of stripe openings through which the growth was seeded. We also investigated a method to separate the completely overgrown layer from the substrate. This mechanical epitaxial lift-off technique may be used for hybrid integration of optoelectronic and electronic devices.

The oxidation of polycrystalline silver films by thermal, ground-state atomic oxygen

Abstract Experimental results indicate a linear relationship between oxide layer thickness and exposure time for thin Ag films exposed to thermal, ground-state atomic oxygen fluxes of the order of 10 17 atoms/(cm 2 s). Exposure times ranged between 10 and 120 s, and all exposures were made at ambient temperature. The techniques of scanning electron microscopy (SEM) and Auger electron spectroscopy (AES) were used to characterize stress-induced damage in the thickest oxide layers. This damage was also observed using RBS (Rutherford backscattering spectroscopy) techniques which were applied to determine oxide layer thicknesses as a function of exposure time. Results are compared with data recently obtained from similar measurements using thin, polycrystalline Cu films.

A computer-automated ion beam channeling system

Abstract A computer-automated ion channeling system has been developed to provide an expanded capability on the RBS beam leg of the Universitys 3 MV Dynamitron accelerator. The basic system components are a PC/AT microcomputer equipped with a multichannel analyzer data acquisition board, motion control system hardware, operating system software (with graphics output capabilities) and associated electronics. Details of the development of this system will be discussed, and initial test results will be presented.

Uniform radial flow epitaxy for thin layer heterostructures

Abstract We describe an epitaxial growth technique called uniform radial flow epitaxy (URFE) for growing thin layer heterostructures of III–V compound semiconductors. The geometry of the URFE reactor is similar to the configuration used in vapor levitation epitaxy (VLE) but the growth vapors are delivered to the top of the substrate which is resting on a paddle. This design allows samples of arbitrary shape to be used while retaining the proven ability of the VLE to grow thin layer heterostructures with abrupt interfaces. The relaxed tolerances of the URFE reactor result in easier fabrication of the quartz reactor. A unique feature of the URFE reactor incorporates an isolating gas curtain between the deposition chambers to assure interface abruptness. Early growths have yielded epitaxial layers of the InP and InGaAs less than 100 A thick with 5%–8% uniformity in layer thickness over 1 inch square samples.

Deep-level transient spectroscopy studies of 2.0 MeV 16O+ ion implanted n-InP

Abstract We have carried out deep-level transient spectroscopy (DLTS) studies of several samples of n-InP implanted with different doses of 2 MeV 16 O + ions to investigate the behavior of deep levels in the near-surface regions of the samples. Results of samples implanted at room temperature show drastic change in the defect structure, with the disappearance of peaks originally present in unimplanted control samples. DLTS studies have also been conducted on hot-implanted n-InP and also on those that have been subjected to rapid thermal annealing (RTA) at 750°C. DLTS results from RTA samples show that there is a certain degree of lattice recovery as shown by the return of electron trapping levels. Rutherford backscattering (RBS) channeling data on RTA samples also show limited lattice recovery in the surface region.