Mid-infrared photoconductive properties of heavily Bi-doped PbTe p–n homojunction diode grown by liquid-phase epitaxy

Abstract

We fabricated a heavily Bi-doped (xBi≈2×1019cm−3) PbTe p–n homojunction diode that detects mid-infrared wavelengths by the temperature difference method (TDM) under controlled vapor pressure (CVP) liquid phase epitaxy (LPE). The photocurrent density produced by the heavily Bi-doped diode sample is approximately 20 times and 3 times greater than that produced by an undoped and heavily In-doped sample, respectively. By varying the ambient temperature from 15K to 225K, the detectable wavelength is tunable from 6.18μm to 4.20μm. The peak shift of the detectable wavelength is shorter in the heavily Bi-doped sample than in the undoped sample, consistent with our previously proposed model, in which Bi–Bi nearest donor–acceptor pairs are formed in the heavily Bi-doped PbTe liquid phase epitaxial layer. Current–voltage (I–V) measurements of the heavily Bi-doped diode sample under infrared exposure at 77K indicated a likely leak in the dark current, arising from the deeper levels. From the dark I–V measurements, the activation energy of the deep level was estimated as 0.067eV, close to the energy of the deep Tl-doped PbTe acceptor layer. We conclude that the deep level originates from the Tl-doped p-type epitaxial layer.