The measurement of the energy distribution of vacuum emitted electrons from InGaN/GaN light-emitting diodes (LEDs) has proven essential in understanding the efficiency loss mechanism known as droop. We report on the measurement and identification of a new low-energy feature in addition to the previously measured three peaks present in the electron emission spectrum from a forward biased LED. Photoemission measurements show that the two low-energy peaks correspond to photoemitted electrons from each of the p-contact metals, palladium and gold. We confirm that the mid and high-energy peaks are due to electrons which have transited the p-type region of the device and have been emitted from the semiconductor surface from the bulk Γ-valley or a high-energy side valley.
Vertical β-Ga2O3 Schottky diodes from metal-organic chemical vapor deposition (MOCVD)-grown epitaxial films are reported in this paper for high-power application devices. The Schottky diode, fabricated with a field termination structure, showed a low differential specific on-resistance of 0.67 mΩ cm2. Furthermore, the MOCVD-grown β-Ga2O3 vertical Schottky diodes exhibited a punch-through breakdown and a higher Baliga's figure-of-merit compared to those from other epitaxial growth methods of similar drift layer thickness. This suggests that the MOCVD growth, supporting high-quality epitaxy, can be promising for high-performance β-Ga2O3-based high-power devices.
Tunnel junctions (TJs) offer alternative designs and promise in some cases improved performances for nitride-based light-emitting diode (LEDs) and laser diodes (LDs) and are widely used in academic studies. However, the voltage penalty of the LEDs and LDs, in comparison with standard contact technologies, has been a major concern especially for commercial applications. In this study, we investigated methods to achieve low excess voltage. Using ammonia molecular beam epitaxy (NH3 MBE), GaN TJs were grown on commercial metalorganic chemical vapor deposition (MOCVD) grown blue LED wafers. Atom probe tomography (APT) and secondary ion mass spectrometry (SIMS) indicate 1 min buffered HF (BHF) clean of the regrowth interface reduced Mg and impurity incorporation into the n++ regrown TJ layers. The wafers were processed and measured in parallel to reference wafers using both university processes and industry processes. At 20 A cm−2, TJ LEDs grown with Si δ-doping at the junction interface processed in the university cleanroom had a forward voltage of 3.17 V in comparison to 2.86 V for LEDs processed with a standard indium tin oxide (ITO) contact. Unencapsulated TJ LEDs processed by industrial process without ITO or current blocking layer had about 0.3 V excess voltage compared to reference LEDs. The TJ LEDs also had more uniform light emission profile. The low excess voltage and consistent results acquired in both settings suggest that TJ can be scaled for industrial processes.
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