INFLUENCE OF BUFFER LAYER AND PROCESSING ON THE DARK CURRENT OF 2.5-MU-M-WAVELENGTH 2-PERCENT-MISMATCHED INGAAS PHOTODETECTORS

An extensive study is presented in which different buffer layers for t he growth of 2.51 mu m wavelength mismatched InGaAs photodetectors are compared. The dark current of the photodetectors is measured to judge the quality of the buffer layers. These differ in material compositio n (InGaAs or InAsP), grading mechanism (linear or stepwise), total buf fer-layer thickness and number of steps. It is shown that the detector s with a thick InAsP buffer, grown on a 2 degrees-off-oriented substra te, lead to the lowest dark currents. Different processing schemes are compared and it is shown experimentally that the dark current of a me sa-type detector consists of a part proportional to the circumference and one proportional to the detector area. The latter part is shown to be equal to the dark current of a planar Zn-diffused detector with th e same dimensions.