H. C. Casey

Refractive index of AlxGa1−xAs between 1.2 and 1.8 eV

The refractive indices of AlxGa1−xAs samples prepared by liquid‐phase epitaxy were determined from accurate double‐beam reflectance measurements. The variation of the refractive index with photon energy at room temperature was obtained for AlAs mole fractions between 0 ≤ x ≤ 0.38 in the spectral range 1.2–1.8 eV.

Evidence for low surface recombination velocity on n‐type InP

A comparison was made of the photoluminescent (PL) intensities of n‐type InP and GaAs at room temperature. The PL intensity for InP was over 100 times greater than for comparably doped GaAs. The effect of surface recombination velocity S on the PL intensity was evaluated numerically. When this evaluation is applied to the PL intensity ratios of n‐type InP and GaAs it shows that S for n‐type InP is sufficiently small to eliminate significant influence of nonradiative surface recombination on the observed PL intensity.

Room-temperature operation of low-threshold separate-confinement heterostructure injection laser with distributed feedback

Separate‐confinement heterostructure injection lasers with periodic corrugations in the optical cavity were prepared by a hybrid liquid phase epitaxy (LPE) and molecular beam epitaxy (MBE) growth process. The N‐Al0.3Ga0.7As, N‐Al0.12Ga0.88As, p‐GaAs active layer, and P‐Al0.12Ga0.88As layers were grown by LPE, a 0.3748‐μm periodic corrugation was ion milled into the P‐Al0.12Ga0.88As layer, and then the P‐Al0.3Ga0.7As and p‐GaAs top layers were grown over the corrugation by MBE. The temperature dependence of the lasing wavelength between 12.6 and 24.8 °C demonstrated the behavior expected for a distributed‐feedback laser. The threshold current density was 2.2 kA/cm2 at room temperature.

Continuous room‐temperature operation of GaAs‐AlxGa1−xAs double‐heterostructure lasers prepared by molecular‐beam epitaxy

The continuous (cw) operation at temperatures as high as 100 °C of stripe‐geometry GaAs‐AlxGa1−xAs double‐heterostructure lasers fabricated by molecular‐beam epitaxial (MBE) techniques has been achieved. Improved MBE laser performance was the result of the extensive efforts to eliminate hydrocarbon and water vapor from the growth apparatus. For 12‐μm‐wide stripe‐geometry lasers with 380‐μm‐long cavities, the cw threshold currents varied between 163 and 297 mA at room temperature.

Investigation of heterojunctions for MIS devices with oxygen‐doped AlxGa1−xAs on n‐type GaAs

Metal‐insulator‐semiconductor (MIS) structures were prepared with high‐resistivity oxygen‐doped Al0.5Ga0.5As layers on n‐type GaAs. These layers were grown by molecular‐beam epitaxy (MBE). Capacitance‐voltage measurements of MIS structures on both conducting and high‐resistivity substrates demonstrate the achievement of deep depletion for reverse‐bias and a near‐flatband condition at zero bias. Measurement of the output characteristics of a majority‐carrier depletion mode MISFET illustrates the application of this MIS technique to three terminal devices. The presence of a 2000‐A‐thick O‐doped Al0.5Ga0.5As layer on n‐type GaAs was found to enhance the photoluminescent intensity of the n‐GaAs layer by 52 times over that of an exposed GaAs surface. The measurements described here demonstrate that the use of single‐crystal lattice‐matched heterojunctions of O‐Al0.5Ga0.5As–n (GaAs) avoids large interface state densities. Admittance spectroscopy measurements permitted assignment of the dominant deep level in O‐...

Reduction of threshold current density in GaAs–Alx Ga1−x As heterostructure lasers by separate optical and carrier confinement

Heterostructure lasers in which the GaAs active layer is bounded on each side by successive layers of AlxGa1−xAs to confine the carriers and AlyGa1−yAs (y>x) to confine the light have been fabricated and studied. Room‐temperature threshold current densities as low as 690 ± 40 A/cm2 with differential quantum efficiencies of 32% have been obtained for 1‐mm cavity lengths.

Dry processing of high resolution and high aspect ratio structures in GaAs-AlxGa 1− xAs for integrated optics

The properties of ion-beam milling, rf-sputter etching, and plasma etching for the fabrication of high resolution integrated optical structures in GaAs and Al(x)Ga(l-x)As were investigated. The ion-beam milling rates for a 500-eV Ar beam were measured as a function of the angle of incidence for A2-1350 photoresist, GaAs, Al, Ti, and Ta in vacuum. For Ti and Ta, the ion-beam milling rates were measured for various O(2) partial pressures in the target chamber. For the fabrication of high-resolution patterns, a technique was developed in which a very thin resist pattern is transferred by plasma etching into a layer of Ta prior to ion-beam milling. Both ion-beam milling and rf-sputter etching through the Ta metal mask were used for the fabrication of gratings in GaAs. From measurements made in this study, it was found that rf-sputter etching in an Ar atmosphere results in a resolution comparable to ion-beam milling at normal incidence, but the material removal efficiency is somewhat lower. Third-order Bragg diffraction gratings (period = 0.36-0.37 microm) for GaAs-Al(x)Gal(1-x) As heterostructure lasers and ridged stripes 10 microm wide and 1.5-2.0 microm deep have been prepared by these techniques. High-aspect ratio or skewed-profile gratings were obtained by selection of the ion-beam milling or rf-sputter etching conditions. As previously reported, these structures have been overgrown by MBE A(x)Gal(1-x) As layers to form distributed feedback lasers.

Use of oxygen‐doped AlxGa1−xAs for the insulating layer in MIS structures

Metal‐insulator‐semiconductor capacitors were prepared by doping an Al0.5Ga0.5As layer with oxygen in order to demonstrate a lattice‐matched single‐crystal insulator‐semiconductor heterojunction. Crystal growth was by molecular‐beam epitaxy. Interface trap effects were not observed in capacitance‐voltage measurements, while the current‐voltage measurements show space‐charge‐limited currents for forward and reverse biases.

Back‐surface emitting GaAsxSb1−x LED’s (λ=1.0 μm) prepared by molecular‐beam epitaxy

Compositionally graded layers of GaAsxSb1−x have been grown on GaAs substrates by molecular‐beam epitaxy. Planar Zn‐diffused 50‐μm‐diam light‐emitting diodes have been prepared in GaAs0.9Sb0.1. The 1.0‐μm wavelength emission was taken out through the transparent GaAs substrate, and for a pulsed current of 100 mA, the external quantum efficiency was 0.1%.

Electrical properties of Ge‐doped p‐type AlxGa1−xAs

The Hall effect and conductivity of Ge‐doped p‐type AlxGa1−xAs has been studied in the temperature range from 77 to 500 K. The experimental results have been analyzed to yield the acceptor and donor concentration and the Ge activation energy. The samples have been found to be heavily compensated with an average compensation ratio of about 0.4. The activation energy was found to increase strongly with Al content for x<0.6 and to decrease with Ge concentration.