III-nitride tunnel diodes with record forward tunnel current density

Abstract

We report on the design, fabrication, and characterization of the first interband tunnel junctions showing forward tunneling characteristics in the III-Nitride system. We have achieved record forward tunneling currents (>100 mA/cm2 at 10 mV, and > 10 A/cm2 peak current) using polarization engineered GaN/InGaN/GaN heterojunction diodes. We also report for the first time, negative differential resistance in interband III-Nitride tunnel junctions, with peak-valley current ratio (PVCR) of up to 5 at room temperature, and 147 at low temperature. Interband tunnel junctions can be utilized to connect multiple active regions devices such as multiple active region emitters and multi junction solar cells, which require efficient reverse tunneling and forward tunneling respectively. Efficient inter-band tunneling has been a challenge in III-Nitrides mainly due to the large band gaps found in this material system, which reduce tunneling probability. Recently, the unique property of polarization in III-nitrides was used to engineer band bending over smaller distances in nitride heterostructures to enhance tunneling [1, 2, 3], and we recently demonstrated a p-GaN/InGaN/n-GaN backward diode with record current density of 118 A/ cm2 at a reverse bias of 1 V where a thin high indium composition InGaN well was used to enhance tunneling between GaN regions [3]. Tunnel junctions are a critical component of multiple junction solar cells, and there is an interest to exploit the large band gap range of III-nitrides in such devices. However, such an application would require forward, rather than reverse tunnel diodes. In this work, we use polarization engineering to design and demonstrate the inter-band forward tunneling diodes with the high current density and low forward voltage drop.