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The recent achievement of p-type AlN films via Be doping was utilized to achieve novel heteroepitaxial diodes with Schottky, Pin, and junction barrier Schottky (JBS) electrical behavior. Although the heteroepitaxial structures were quasi-vertical, which is subject to many issues lowering the breakdown voltage, the Pin diode achieved a breakdown voltage of ∼25 V for a 200 nm thick unintentionally doped intrinsic layer indicating ∼50% of the theoretical breakdown voltage performance for a similar homoepitaxial GaN pin diode. JBS and Schottky diodes were implemented using the inherent and intentional stress cracking properties of AlN grown on GaN films avoiding regrowth and plasma etching, both known to be technology impediments. The density of the intentional cracks and crystalline quality of the p-AlN films was controlled via Be doping and the total metal dose supplied during the metal modulated epitaxy shutter cycle resulting in differing degrees of grown stress. Since the intentional crack density determines the surface area ratio of the Schottky diode to the Pin diode, it is a key design parameter in optimizing device performance. Furthermore, a novel current spreading layer was implemented to improve the current uniformity in these devices. The high breakdown voltage and good forward voltage characteristics of these devices shows potential to enable high-performance III-nitride high-power devices. [ABSTRACT FROM AUTHOR]

Semi-insulating GaN films with controlled dopant profiles have significant potential to improve the performance of high-power electronics. Beryllium doped GaN (GaN:Be) films previously demonstrated a semi-insulating nature, but the Be-dopant profiles in these films exhibited Be surface segregation and accumulation, which would lead to undesired leakage current paths in devices and deterioration of breakdown voltage. Improved growth kinetics of metal modulated epitaxy at low growth temperatures are applied in the study of GaN:Be films to achieve selectively controlled and abrupt step-doped Be profiles. The GaN:Be films were found to be semi-insulating via Hall effect measurements at elevated temperatures of 495 K. The films were shown to effectively electrically compensate surface contaminants at regrowth interfaces. Surface contaminants (O, Si, and C) typically result in unintentional n-type doping at the GaN on GaN regrowth interface. In order to demonstrate the utility of Be doping, GaN:Mg p-type films are grown atop GaN:Be buffer, AlN buffer, and control samples without any insulating buffer on GaN:Fe templates. Remarkably, the p-type films grown atop control samples up to 400 nm thick are compensated from surface contaminants, whereas the films grown atop AlN and GaN:Be insulating layers effectively electrically neutralize the surface contaminants and result in high hole concentrations of 2.3 and 2.5 × 1019 cm−3, respectively. The use of GaN:Be instead of AlN buffers eliminates the need to deconvolve the effects of the AlN/GaN 2D sheet charges and defects from lattice mismatch, removes lateral conduction paths, and reduces inherently high static vertical electric fields that detract from power device performance. [ABSTRACT FROM AUTHOR]

The use of beryllium as both an i-layer and current spreading layer (CSL) dopant in GaN quasi-vertical p-i-n diodes on sapphire was investigated. With the inclusion of the Be CSL, the current uniformity dramatically improves from $\sim 40$ % of the p-contact radii to 100% resulting in higher breakdown performance and reduced leakage currents. Metal modulated epitaxy (MME) GaN p-i-n diodes on sapphire templates with beryllium-doped GaN (GaN:Be) i-layer thicknesses in the range of 1– $10~\mu \text{m}$ are reported. Additionally, a GaN:Be CSL sandwiched between two conductive Si-doped GaN layers is used to achieve a high quasi-vertical p-i-n diode breakdown voltage of 375 V and a breakdown field of 1.875 MV/cm for the $2~\mu \text{m}$ i-layer p-i-n diodes. At room temperature, the diode with a mesa diameter of $100~\mu \text{m}$ showed a differential ON-resistance (${R}_{ \mathrm{\scriptscriptstyle ON}} \,\,=\,\,\text{d}{V}/\text{d}{I}$) as low as 0.3 $\text{m}\Omega $ -cm2 for a $10~\mu \text{m}$ GaN:Be i-layer diode. A Baliga’s figure of merit (BFOM) ($\text {V}_{\text {Br}}^{{2}}/{R}_{ \mathrm{\scriptscriptstyle ON}}$) of 363 MW/cm2 was achieved for the $10~\mu \text{m}$ i-layer p-i-n diode. This is the highest reported BFOM for GaN p-i-n diodes on foreign substrates. Additionally, the leakage current density is very low: $1\times 10^{{-{9}\,\,{ }}}$ kA/cm2 at 300 V reverse bias for the 5 and $10~\mu \text{m}$ GaN:Be i-layer devices. These devices exhibit a current ON/ OFF ratio ten orders of magnitude. Given the low particle environment, rapid growth rates, ease of compatibility with the toxic dopant Be, and high device performance, the use of Be as a dopant is very useful for high-power devices. [ABSTRACT FROM AUTHOR]