p-InGaN/n-GaN heterojunction diodes and their application to heterojunction bipolar transistors

p-InGaN/n-GaN heterojunction diodes were grown by metalorganic vapor phase epitaxy and characterized using current-voltage (I-V) and capacitance-voltage (C-V) measurements. We changed the In mole fraction in p-InGaN from 0 to 25% to investigate diode characteristics. All the diodes showed rectified I-V characteristics at room temperature. The ideality factors obtained from forward I-V characteristics were around 2, meaning that the recombination current is dominant instead of the tunneling current through the defects in depletion layers of the diodes. The breakdown voltage in reverse I-V characteristics depends on the net donor concentration (N_D - N_A) in n-GaN instead of the In mole fraction in p-InGaN. This result also means that the defects in p-InGaN do not influence the breakdown voltage. The built-in potential from C-V measurements decreases with the In mole fraction in p-InGaN, meaning that the valence band discontinuity increases with the In mole fraction. This valence band discontinuity realizes the hole confinement in an HBT with an p-InGaN base. Using these InGaN/GaN heterojunction diodes, an InGaN/GaN double heterojunction bipolar transistor was fabricated for the first time. The maximum current gain of 1.2 was obtained at room temperature.