Contents I. Introduction
Ternary indium gallium nitride (InGaN) alloys are the main building blocks for light-emitting diodes (LEDs) and laser diodes. Their inherent properties, such as their direct bandgap, tunable from 0.64 to 3.38 eV [1], [2], high absorption coefficient [3], [4], and radiation resistance [5], also make InGaN compound semiconductors an excellent candidate for photovoltaic applications. Despite the superior properties of InGaN, there are still many roadblocks to achieving high-efficiency solar cells. One bottleneck limiting the performance of such devices arises from the potential barrier in the GaN/InGaN heterointerface due to the electron affinity difference between InN and GaN [6]. Another important factor influencing the photovoltaic properties of III-nitride solar cells is the existence of significant interface charges induced by spontaneous and piezoelectric polarizations [7]–[9]. A method to overcome these constraints is by using InGaN homojunction structures instead of InGaN/GaN heterostuctures. Although InGaN homojunction devices are predicted to achieve greater photovoltaic properties than their heterojunction counterparts [10], experimental evidence proved the opposite mainly due to the difficulty of growing high-quality p-InGaN layers [11]. It was not until very recently that p-i-n InGaN homojunctions with high indium content and reduced stacking fault density were reported [12], underling that there is still a lot to be done toward efficient InGaN-only photovoltaics.
