High-pressure MOCVD growth of InGaN thick films toward the photovoltaic applications.

ABSTRACT

The highly efficient photovoltaic cells require the In-rich InGaN film with a thickness more than 300 nm to achieve the effective photo⋅electricity energy conversion. However, the InGaN thick films suffer from poor crystalline quality and phase separations by using the conventional low-pressure metal organic chemical vapor deposition (MOCVD). We report on the growth of 0.3-1 µm-thick InGaN films with a specially designed vertical-type high-pressure MOCVD at the pressure up to 2.5 atms. The In incorporation is found to be greatly enhanced at the elevated pressures although the growth temperatures are the same. The phase separations are inhibited when the growth pressure is higher than atmospheric pressure, leading to the improved crystalline quality and better surface morphologies especially for the In-rich InGaN. The In0.4Ga0.6N with the thickness of 300 nm is further demonstrated as the active region of solar cells, and the widest photoresponse range from ultraviolet to more than 750 nm is achieved.