MBE-grown HgCdTe multi-layer heterojunction structures for high speed low-noise 1.3–1.6 µm avalanche photodetectors

HgCdTe is an attractive material for room-temperature avalanche photodetectors (APDs) operated at 1.3–1.6 µm wavelengths for fiber optical communication applications because of its bandgap tunability and the resonant enhancement of hole impact ionization for CdTe fractions near 0.73. The HgCdTe based separate absorption and multiplication avalanche photodetector is designed and fabricated for backside illumination through a CdZnTe substrate. The multi-layer device structure is comprised of seven layers including 1). n ⁺ contact 2). n ^? diffusion buffer 3). n ^? absorber 4). n charge sheet 5). n ^? avalanche gain 6). p to form junction, and 7).p ⁺ contact. Several wafers were processed into 45 µm × 45 µm and 100 (µm × 100 µm devices. The mean value of avalanche voltage is 63.7 V measured at room temperature. At 1 GHz, the device shows a gain of about 7 for a gain-bandwidth product of 7 GHz. This first demonstration of an all molecular beam epitaxially grown HgCdTe multi-layer heterojunction structure on CdZnTe substrates represents a significant advance toward the goal of producing reliable room temperature HgCdTe high speed, low noise avalanche photodetectors.