Record high gain from InAs avalanche photodiodes at room temperature

Abstract

Avalanche photodiodes (APD) are important components in short-wave and mid-wave infrared detection systems (imaging, laser radar, communications, etc.) because their internal gain can improve receiver sensitivity and enables the detection of weak photon fluxes. The statistical nature of impact ionization in APDs contributes to excess shot noise, however. The excess noise factor, F(M), is related to the ratio of the electron and hole ionization coefficients, k, and multiplication, M, by F(M) = <;M<;sup>2<;/sup>>/<;M><;sup>2<;/sup> = k<;M> + (1-k)(2-1/<;M>). In the mid-infrared, HgCdTe APDs represent the current state-of-the-art; at liquid nitrogen temperatures, advanced devices offer excellent low noise characteristics with F(M) ~ 1, gains of >1000, and excellent dark currents. Unfortunately, devices that operate at shorter wavelengths exhibit degraded noise characteristics and significantly lower maximum gains <;30. This, when combined with the growth and fabrication challenges associated with II-VI compounds has motivated the search for alternative APD materials. InAs APDs, which offer a shorter wavelength cutoff wavelength of ~3 μm, have recently been found to exhibit F(M) ~ 1, with moderately low dark current at room temperature. Increasing the multiplication region thickness increases the gains achievable at low bias, which is beneficial for integration with Read Out-Integrated Circuits (ROICs). Therefore, to design a high-gain InAs APD, a thick multiplication region is required. This, in turn, necessitates extremely low background doping (<;1015 cm-3), or appropriate counter doping, in order to realize complete depletion and a uniform electric field profile. In this paper, we report record high-gain InAs APDs employing 6 μm-thick and 10 μm-thick intrinsic regions with low background doping of ~4×1014 cm-3, as determined by C-V profiling. An AlAsSb blocking layer was used in both structures to suppress electron diffusion current, the dominant dark current mechanism at room temperature. Significant reduction in dark current were critical to characterize these thicker multiplication regions at high gain, resulting in record high room temperature multiplication gain of ~300 at 15 V bias. This is ~6× the previous record for InAs of 50 at 15 V, as well as significantly higher than the maximum gain of 126 reported at higher biases, and represents a significant step forward in InAs APD performance.