MBE growth of HgCdTe avalanche photodiode structures for low-noise 1.55 μm photodetection

Abstract

Molecular-beam epitaxy (MBE) has been utilized to fabricate HgCdTe heterostructure separate absorption and multiplication avalanche photodiodes (SAM-APD) sensitive to infrared radiation in the 1.1–1.6 μm spectral range, as an alternative technology to existing III–V APD detectors. Device structures were grown on CdZnTe(211)B substrates using CdTe, Te, and Hg sources with in situ In and As doping. The composition of the HgCdTe alloy layers was adjusted to achieve both efficient absorption of IR radiation in the 1.1–1.6 μm spectral range and low excess-noise avalanche multiplication. The Hg 1− x Cd x Te alloy composition in the gain region of the device, x=0.73, was selected to achieve equality between the bandgap energy and spin–orbit splitting to resonantly enhance the impact ionization of holes in the split-off valence band. The appropriate value of this alloy composition was determined from analysis of the 300 K bandgap and spin–orbit splitting energies of a set of calibration layers, using a combination of IR transmission and spectroscopic ellipsometry measurements. MBE-grown APD epitaxial wafers were processed into passivated mesa-type discrete device structures and diode mini-arrays using conventional HgCdTe process technology. Device spectral response, dark current density, and avalanche gain measurements were performed on the processed wafers. Avalanche gains in the range of 30–40 at reverse bias of 85–90 V and array-median dark current density below 2×10 −4 A/cm 2 at 40 V reverse bias have been demonstrated.