Direct visualization of the N impurity state in dilute GaNAs using scanning tunneling microscopy

Abstract

The interaction between nitrogen (N) impurity states in III-V compounds plays a key role in controlling optoelectronic properties of the host materials. Here, we use scanning tunneling microscopy to characterize the spatial distribution and electronic properties of N impurity states in dilute GaNAs. We demonstrated that the N impurity states can be directly visualized by taking empty state current images using the multipass scanning method. The N impurity states broadened over several nanometers and exhibited a highly anisotropic distribution with a bowtie-like shape on the GaAs(110) surface, which can be explained by anisotropic propagation of strain along the zigzag chains of Ga and As atoms in the {110} plane. Our experimental findings provide strong insights into a possible role of N impurity states in modifying properties of the host materials.

Spatially resolved electronic structure of an isovalent nitrogen center in GaAs

“…[49,50] the peak position of the single nitrogen level in general shows up between +1.2 and +1.7 V. As illustrated well by the spectroscopy series of Ishida et al, the observed values in STS are dependent on the tip condition, hence, we are reluctant to compare the exact values resulting from STS. The difference observed with our value is most probably due to the use of illumination and a more intrinsic environment in our case.…”

“…In previous X-STM measurements at room temperature [45][46][47][48] these features were not observed. A recent publication on X-STM measurements at 77 K reports a feature similar to B1 and B2, although the structure of the features was less clearly resolved [50]. Discussion of both B1 and B2 will be continued later.…”

“…When imaging at +0.60 V sample bias [see Fig [50]. As will be discussed later, these features are related to nitrogen substituting for arsenic atoms in different planes below the surface, where the labels 0 to 4 indicate the distance from the (110) cleavage surface in number of planes.…”

“…For every depth of the nitrogen below the surface, including the surface nitrogen, a resonance in the voltage-dependent contrast intensity is found. Ishida et al also suggested that a trend of resonance voltage with depth could be present as they saw a shift in the differential tunneling conductance spectra when comparing the fourth and seventh layer features [50]. A Voigt profile is used to get an estimate of the voltage at which the resonance occurs (see Supplemental Material S1 [53]).…”

“…X-STM has been applied successfully in the past to image nitrogen atoms in GaAs as atomically sized features and determine the distribution of nitrogen in various structures such as quantum wells [45][46][47][48][49]. However, until recently little attention has focused on the imaging of the electronic state of nitrogen [50].…”