Effective mass filtering: Giant quantum amplification of the photocurrent in a semiconductor superlattice

Abstract

We report the first observation of an extremely large photocurrent amplification phenomenon at very low voltages in a superlattice of Al_0.48In_0.52As (35 Å)/Ga_0.47In_0.53As (35 Å), grown by molecular beam epitaxy. Responsivities at λ=1.3 μm are as high as 4×10³ A/W at 1.4 V corresponding to a current gain of 2×10⁴. Significant gains (≂50) were obtained at voltages as low as 20 mV. The detectivity D* at λ=1.3 μm and 1‐kHz modulation frequency is 10¹¹ (cm Hz^1/2/W) at 0.2‐V bias. This effect, which represents a new quantum type photoconductivity, is caused by the large difference in the tunneling rates of electrons and holes through the superlattice barriers, associated with their large effective mass difference (effective mass filtering). Superlattice effective mass filters represent a new class of low voltage, high gain photodetectors. A unique feature, which makes them potentially extremely versatile, is the ability to tune the gain and gain‐bandwidth product over a wide range by varying the superlattice period and/or duty factor.