Solar-blind AlxGa1–xN (x > 0.45) p–i–n photodiodes with a polarization-p-doped emitter

Abstract

Polarization-induced p-type doping of AlGaN layers with high aluminum content during plasmaassisted MBE growth has been studied. It is shown that a gradient of the AlN molar fraction in AlGaN (composition gradient) on a level of 0.005 nm^–1 must be set in order to obtain a hole concentration of ~10¹⁸ cm^–3 (measured by the C–V method) in Al_xGa_1–xN:Mg (x = 0.52–0.32) layers with dopant concentration [Mg] = 1.3 × 10¹⁸ cm^–3. p–i–n photodiodes based on AlGaN heterostructures with such layers as p-emitters showed maximum photoresponsitivity in the solar-blind wavelength range (λ = 281 nm) about 35 and 48 mA/W at reverse bias voltage U = 0 and–5 V, respectively, and exhibited a dark current density of 3.9 × 10^–8 A/cm² at U =–5 V.