Abstract: A p-i-n photodiode having a high responsivity and quantum efficiency due to an AlGaN heterojunction where photons are absorbed within the p-n junction thereby eliminating carrier losses due to surface recombination and diffusion processes. Ultraviolet light comes through a transparent substrate, such as sapphire, a transparent AlN buffer and an n-doped AlGaN layer, and to an undoped AlGaN layer where the light is absorbed. The undoped layer is sandwiched between the n-doped AlGaN layer and a p-doped AlGaN layer. Metal contacts are formed on the doped layers to obtain the current caused by the absorbed light in the undoped layer. The mole fractions of the Al and Ga in the undoped and doped layers may be adjusted to obtain a desired wavelength bandpass of light to be detected.

Abstract: A GaN/AlGaN heterojunction bipolar phototransistor having AlGaN contact, i-GaN absorbing, p-GaN base and n-GaN emitter layers formed, in that order, on a UV transparent substrate. The phototransistor has a gain greater than 10.sup.5. From 360 nm to 400 nm, eight orders of magnitude drop in responsivity was achieved. The phototransistor features a rapid electrical quenching of persistent photoconductivity, and exhibits high dark impedance and no DC drift. By changing the frequency of the quenching cycles, the detection speed of the phototransistor can be adjusted to accommodate specific applications. These results represent an internal gain UV detector with significantly improved performance over GaN based photo conductors.