GaN:Be I-Layer-Based High-Power p-i-n Diodes Achieving Large Quasi-Vertical MBE Breakdown Performance

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 similar to 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 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 m i-layer p-i-n diodes. At room temperature, the diode with a mesa diameter of 100 mu m showed a differential ON-resistance (R-ON = dV/dI) as low as 0.3 m Omega-cm(2) for a 10 mu m GaN:Be i-layer diode. A Baliga's figure of merit (BFOM) (V-Br(2)/R-ON) of 363 MW/cm(2) was achieved for the 10 mu 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 x 10(-9) kA/cm(2) at 300 V reverse bias for the 5 and 10 mu 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.