Direct Evidence for Shallow Acceptor States with Nonspherical Symmetry in GaAs

Abstract

We investigate the energy and symmetry of Zn and Be dopant-induced acceptor states in GaAs using cross-sectional scanning tunnelling microscopy (STM) and spectroscopy at low temperatures. The ground and first excited states are found to have a nonspherical symmetry. In particular, the first excited acceptor state has a T(d) symmetry. Its major contribution to the STM empty-state images allows us to explain the puzzling triangular shaped contrast observed in the empty-state STM images of acceptor impurities in III-V semiconductors.

Ultrafast evolution of photonic eigenstates in k-space

“…This relation is usually not straightforward: owing to the imposed periodicity, bands are folded into every Brillouin zone, inducing splitting of bands and the appearance of bandgaps. As a result, exciting phenomena such as negative refraction 6,7 , autocollimation of waves 8,9 and low group velocities 10-12 arise. k-space investigations of electronic eigenstates have already yielded new insights into the behaviour of electrons at surfaces and in novel materials [13][14][15][16] .…”

Surface Induced Asymmetry of Acceptor Wave Functions

“…The surface, however, is known to strongly influence the properties of an impurity close to the surface [8], and thus a central question for all such surface measurements via cross-sectional scanning tunneling microscopy (XSTM) is how closely the local density of states (LDOS) is related to properties of an impurity in the bulk. Several groups have interpreted the XSTM contrast of acceptors as being directly related to the wave function of the impurity state [2,3,5,6], while others have proposed that highly asymmetric observed acceptor shapes arise from hybridization of the impurity state with excited states [4] or intrinsic surface states [9].…”

“…In the past decade many groups have scrutinized at the atomic scale the electronic and spectroscopic details of individual impurities, such as Si, Zn, and Mn, embedded in the topmost layers of a cleaved semiconductor crystal like GaAs or InAs [1][2][3][4][5][6]. A correct interpretation of these atomistic properties is essential for a proper understanding of the macroscopic properties of doped materials.…”

Band structure related wave-function symmetry of amphoteric Si dopants in GaAs

“…For donors only radially symmetric features have been reported [1,2,3,4]. All investigated acceptors exhibit distinct anisotropic features for certain tunneling conditions [5,6,7,8,9,10,11]. Either triangular shaped or bow-tie like contrasts are imaged.…”