Electric field broadening of arsenic donor states in strongly compensated n-type Ge :(As, Ga)

We discuss on the broadening of ground-state to bound excited-state transit ions of shallow donors in strongly compensated n-type Ge in the presence of electric fields and their gradients arising from randomly distributed ioni zed impurities. Low-temperature (T = 3.2 K) far-infrared absorption spectra of strongly compensated n-type Ge:(As,Ca) have been obtained for samples h aving ionized impurity concentration N-I = 2.2 x 10(13)-2.6 x 10(14) cm(-3) . Absorption peaks corresponding to 1s-2p (+/-) transition of arsenic impur ities are observed, and broadened linearly with the ionized impurity concen tration due to interactions between electrons and the quadrupole moments: o f ionized donors. The slope of the peak line width plotted against N-I chan ges at NI approximate to 8 x 10(13) cm(-3) due to the transition of ionized impurity distribution from random (N-I < 8 x 10(13) cm(-3)) to correlated (N-I > 8 x 10(13) cm(-3)). (C) 2001 Elsevier Science B.V. All rights reserv ed.