D.K. Wagner

Antiphase boundaries in GaAs

Antiphase boundaries in GaAs have been produced by growing the GaAs on {001} Ge substrates. The GaAs was grown by the technique of organometallic vapor phase epitaxy to a thickness in excess of 1 μm. The antiphase boundaries are shown to be faceted with facets parallel to the {110} planes being particularly common. The rigid‐body translation at the different facet planes is shown to be small for the {110} planes but it can be large for other facet planes.

Improved photoluminescence of organometallic vapor phase epitaxial AlGaAs using a new gettering technique on the arsine source

Using an aluminum‐gallium‐indium ternary melt for the removal of oxygen and moisture from the arsine source, substantial improvement in the quality of organometallic vapor phase epitaxial AlGaAs can be achieved. The arsine is bubbled through the ternary melt at room temperature prior to its introduction into a low‐pressure reactor. Low‐temperature photoluminescence spectra indicate an improvement in the sharpness of the bound exciton transition after the use of this gettering technique.

Graded band-gap p/n AlGaAs solar cells grown by organometallic vapor phase epitaxy

The growth of p/n graded band‐gap AlGaAs/GaAs solar cells by organometallic vapor phase epitaxy is reported. The best performance is obtained for a cell with the emitter graded from 0 to 45 at. % aluminum over a distance of 0.3 μm. The corresponding solar cell parameters are Isc=27.3 mA/cm2, Voc=1.01 V, and FF=0.73 at 1 sun AM0, corresponding to a conversion efficiency of 14.7%.

Characterization of APBs in GaAs Grown on Si and Ge

Antiphase boundaries are observed in epilayers of GaAs grown by organometallic vapor phase epitaxy on Ge substrates and are then invariably found to show a tendency to facet. Stacking-fault-like fringes caused by the translation of adjacent grains give the information on the relative displacement of the two grains at these interfaces and show that this translation does not have a fixed magnitude for a particular interface but varies with the orientation of the interface. Preferred orientations of the antiphase boundaries and the rigid-body translations have been studied using transmission electron microscopy. Interactions between antiphase boundaries and interfaces have been examined here in heterolayer structures consisting of alternating layers of GaAs and Al x Ga l−x As grown on an (001) Ge substrate. The possibility of using atomic-resolution imaging to investigate the atomic structure of APBs is illustrated and the images are compared with those predicted by image simulation.

Growth of GaAs bicrystals

Bicrystals of gallium arsenide have been grown by the technique of organometallic, vapor phase epitaxy on substrates cut from Czochralski‐grown germanium bicrystals. Both 〈110〉 and 〈001〉 tilt boundaries have been grown. Experimental illustrations of the Σ=3 and Σ=5 grain boundaries are presented. The grain boundaries tend to facet along well‐defined planes but closely reproduce the misorientation of the seed bicrystal.

Study of grain boundaries in GaAs by scanning light microscopy

Abstract Scanning light microscopy was used to investigate the electronic properties of gain boundaries in GaAs. Measurements of the short-circuit photocurrent across the grain boundary in bicrystal specimens reveal directly the presence or abscence of internal electric fields at the boundary. It was found that when fields are present the I–V characteristic is non-ohmic and when they are absent it is ohmic. In the non-ohmic case there is a substantial potential barrier (0.8 eV) at the grain boundary, the height of which is determined by a study of the zero-bias resistance as a function of temperature. The diffusion of minority carriers to the edge of the space charge region assciated with the barrier is observed directly in the structure of the photocurrent, allowing a directly determination to be made of the minority carrier diffusion length adjacent to the grain boundary. The behaviors of photovoltage and photocurrent under bias are also discussed, and it is shown that the latter yields information about the barrier height associated with the normally depleted surface.

High-resolution optical methods for characterization of polycrystalline GaAs thin films

Two optical characterization techniques capable of high lateral spatial resolution (∼ 1 µm) are described and applied to the investigation of polycrystalline GaAs. The first technique yields the minority-carrier diffusion length and is based on a measurement of the change in photocurrent collected at a semitransparent Schottky barrier as reverse bias is varied. The second involves a measurement of photoluminescence intensity. The methods yield information about grain boundaries and granular properties, are compatible with conducting substrates, are nondestructive, and have potential for rapid data acquisition.