Wide gap II-VI diodes with PbTe nano-inclusions for infrared detection and photovoltaics

Abstract

We report on the fabrication and characterization of p–n diodes made from wide bandgap II-VI semiconductors (p-ZnTe/n-CdTe) containing nano-inclusions of narrow bandgap material (PbTe). The diodes are fabricated by molecular beam epitaxy on semi-insulating GaAs (100) substrates. The PbTe nano-inclusions are formed either as a single layer of PbTe with a thickness of 350 nm or as multilayers built from alternating thin layers of PbTe and CdTe. Comparison of cross-sectional scanning electron microscope images with electron beam-induced current measurements confirms that the PbTe nano-inclusions are located in depletion regions of the diodes. Despite the presence of the highly conductive, narrow bandgap PbTe semiconductor between the p- an n-type layers, the current–voltage (I–V) characteristics of the devices show rectifying behavior and acceptable diode parameters in the wide temperature range of 60–290 K. The p-ZnTe/n-CdTe diodes with PbTe nano-inclusions exhibit significant sensitivity to infrared radiation starting at the wavelength of about 1.5 μm and with a long-wavelength cutoff of 3.9 and 5.4 μm at 290 and 50 K, respectively. A peak sensitivity appears at a wavelength of 2.29 μm and reaches the maximum of almost 1 V/W at a temperature of 150 K. The temperature dependence of the cutoff wavelength clearly shows that the sensitivity to infrared radiation of the wide bandgap p-ZnTe/n-CdTe diodes is due to band-to-band optical excitations taking place in PbTe nano-inclusions. The results presented here prove that such diodes can be used for infrared sensing or for two-color infrared solar cells.