High-performance AlGaN Heterojunction Phototransistor with Dopant-free Polarizationdoped P-base

A dopant-free p-type AlxGa1–xN (x = 0.1~0) layer, achieved by polarization induced three-dimensional hole gas, was introduced into the structure of AlGaN npn heterojunction phototransistors (HPTs) as the p-base. The fabricated HPTs with a junction diameter of $150~\mu \text{m}$ exhibit a sharp cutoff with a 360/375-nm rejection ratio of more than 3 orders of magnitude and a responsivity of $5\times 10^{{3}}$ A/W at 360 nm under the 2 V collector bias. A high optical gain of $6.5\times 10^{{4}}$ was obtained at 10 V bias. These results demonstrate the feasibility of polarization-doped p-base in developing high-performance AlGaN UV HPTs.