MOCVD Growth and Characterization of Be-Doped GaN.

Beryllium has been considered a potential alternative to magnesium as a p-type dopant in GaN, but attempts to produce conductive p-GaN:Be have not been successful. Photoluminescence studies have repeatedly shown Be to have an acceptor level shallower than that of Mg, but deep Be defects and other compensating defects render most GaN:Be materials n-type or semi-insulating at best. Previous reports use molecular beam epitaxy or ion implantation to dope GaN with Be, almost exclusively. Due to the high toxicity of Be organometallics, reports of GaN:Be by metal-organic chemical vapor deposition (MOCVD) have been largely absent. Here, we report a systematic study of growth of GaN:Be by MOCVD. All doped samples show the established UV band and yellow luminescence signature of GaN:Be, and growth conditions resulting in high-quality GaN with stable Be incorporation were established. Our results show that the MOCVD growth technique allows for Be incorporation pathways that have not been possible with previous growth methodologies and is highly promising in achieving p-type conductivity in GaN:Be.

Hillock assisted p-type enhancement in N-polar GaN:Mg films grown by MOCVD.

We report on the enhanced incorporation efficiency of magnesium dopants into facets of hexagonal hillock structures in N-polar GaN, studied by comparative analysis of GaN:Mg films grown by MOCVD on high and low hillock density GaN template layers. Total magnesium concentration in planar regions surrounding a hillock structure is comparable to that within hillock sidewall facets measured at 1.3 × 1019 cm-3 by atom probe tomography, and clustering of Mg atoms is seen in all regions of the film. Within individual hillock structures a decreased Mg cluster density is observed within hillock structures as opposed to the planar regions surrounding a hillock. Additionally, the Mg cluster radius is decreased within the hillock sidewall. The favorable incorporation of Mg is attributed to Mg dopants incorporating substitutionally for Ga during growth of semi-polar facets of the hillock structures. Enhanced p-type conductivity of GaN:Mg films grown on high hillock density template layers is verified by optical and electrical measurement.

Pulsed characterization of a UV LED for pulsed power applications on a silicon carbide photoconductive semiconductor switch.

The electrical and optical characteristics of a high-power UV light emitting diode (LED) (365 nm wavelength) were evaluated under pulsed operating conditions at current amplitudes several orders of magnitude beyond the LED's manufacturer specifications. Geared towards triggering of photoconductive semiconductor switches (PCSSs) for pulsed power applications, measurements were made over varying pulse widths (25 ns-100 µs), current (0 A-250 A), and repetition rates (single shot-5 MHz). The LED forward voltage was observed to increase linearly with increasing current (∼3.5 V-53 V) and decrease with increasing pulse widths. The peak optical power observed was >30 W, and a maximum system efficiency of 23% was achieved. The evaluated LED and auxiliary hardware were successfully used as the optical trigger source for a 4H-SiC PCSS. The lowest measured on-resistance of SiC was approximately 67 kΩ.