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While metal-rich ScAlN epitaxy has traditionally led to mixed phase films by controlling the surface chemistry with transient metal doses utilizing a pulsed method of molecular beam epitaxy, phase-pure, metal-rich epitaxy of ScAlN was demonstrated, showing improved structural and electrical characteristics. The effects of substrate temperature and III/V ratio were studied, and an x-ray diffraction figure of merit and surface roughness as low as 225 arcsec and 0.68 nm, respectively, were demonstrated. A significant catalytic effect is observed with the use of Sc in metal-rich conditions, resulting in varied growth rates with substrate temperature and Sc surface coverage. This catalytic effect results in complications when selecting synthesis conditions and for in situ monitoring and can be accounted for improved phase purity. The variation of growth rates with Sc surface coverage introduces non-linearities to the transient initiation stage of growth but also introduces a feedback stabilization of the surface chemistry. Accounting for these complexities, a Sc0.2Al0.8N high electron mobility transistor (HEMT) heterostructure is demonstrated with a sheet resistance of 152 Ω/□, a mobility of 700 cm2/Vs, and a sheet charge of 5.9 × 1013 cm−2. [ABSTRACT FROM AUTHOR]

The structural quality of indium-rich Al0.3In0.7N grown by metal modulated epitaxy (MME), previously demonstrating x-ray diffraction (XRD) figures of merit ∼11 times better than the previous literature is investigated to explain the origin of such a large quality improvement. Four-dimensional scanning transmission electron microscope was used to map the lattice parameter near the AlInN/GaN heterojunction and indicate a 5.4% lattice constant change, suggesting 75% relaxation within ∼2 nm from the interface. Cross-sectional TEM Moiré fringes are observed at the AlInN/GaN heterointerface, indicating that there are misfit dislocations between AlInN and GaN which, while rare, have been observed for other highly mismatched In-rich III-Nitrides. The TEM measurements show regions of contrast indicating larger scale variations in strain, but defect contrast associated with dislocations and/or intrinsic basal stacking faults was minimal, indicating a good quality AlInN film and confirming prior XRD results. Significant electron beam induced damage can occur and depended strongly on operational conditions. The damage threshold current density was estimated using time-dependent TEM to be ∼5.7 A/cm2, significantly lower than from prior studies of InGaN. Damage also strongly depends on the thickness of the TEM foil examined and occurred at thicknesses greater than found for InGaN. The present study suggests that the MME technique is an excellent candidate for growing high-quality indium-rich AlInN films as compared to the traditional molecular beam epitaxy or metal organic chemical vapor deposition techniques. [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]