Physics of imagingp−njunctions by scanning tunneling microscopy and spectroscopy

Abstract

Combined voltage-dependent scanning tunneling microscopy ͑STM͒ images with atomic resolution, local scanning tunneling spectroscopy, and simulations of the potential distribution in the interface-STM tip system are used to extract the physical imaging mechanisms of GaAs p-n interfaces in STM images. It is shown that ͑i͒ the tip-induced changes of the potential near the interface result in the tunneling characteristics of the p-type (n-type͒ layer being dragged into the interfaces' depletion region at positive ͑negative͒ sample voltage. ͑ii͒ This leads to a considerable reduction of the apparent width of the image of the depletion zone in STM images. ͑iii͒ At small negative sample voltages, a pronounced depression line appears. The depression is directly correlated with the electronic interface. It arises from the interplay of competing current contributions from the valence and conduction bands. This understanding of the imaging process allows us to develop methods on how to extract accurate physical data about the properties of the electronic interfaces from scanning tunneling microscopy images.

Structure and electronic spectroscopy of steps on GaAs(110) surfaces

“…6(b), for surface locations opposite the apex of the probe-tip]. It has recently been demonstrated that this sort of accumulation in the CB is greatly restricted by the presence of the GaAs(110) X-point surface states, 13,14 and such states are fully included in our computations. Within our electrostatic model, the charge on the step is thusly determined, and it turns out to be about 0.25 electrons per unit cell (0.40 nm) along the step edge for the situation we are considering in Fig.…”

Non‐polar group‐III nitride semiconductor surfaces

“…For details of the calculation, see Refs. [22,61]. again much larger as compared with those of the filled states, the latter exhibiting again only a very weak dispersion.…”

Spontaneous 2D Accumulation of Charged Be Dopants in GaAsp−nSuperlattices

“…Figure 1(a) shows an example of an XSTM image of several Be and Si-doped layers each with a nominal thickness of 50 nm. The p and n-doped regions are separated by darker lines, which arise from the depletion zones at the interfaces [2]. Although every layer should have the same thickness, the p-doped (brighter) layers are found to be enlarged by as much as 25% compared to the n-doped (darker) layers.…”

“…1(a) shows that each p-type layer exhibits the same brightness in contrast in the center as well as near the interface regions. This indicates that the whole enlarged layer is now p type [2] including the edges near the interface regions, which were originally n doped. Thus, the diffusion of Be dopants leads not only to a compensation of the neighboring Si-doped regions by forming electrically inactive donor-acceptor complexes, but also to an overcompensation by introducing additional electrically active Be dopants.…”

“…The cross-sectional STM method allows us, however, to probe electronic properties with atomic resolution, such as the type of majority carriers [2] as well as the positions and charge states of individual dopants [6]. For example, the STM image in Fig.…”