Simple and efficient scanning tunneling luminescence detection at low-temperature

We have designed and built an optical system to collect light that is generated in the tunneling region of a low-temperature scanning tunneling microscope. The optical system consists of an in situ lens placed approximately 1.5 cm from the tunneling region and an ex situ optical lens system to analyze the emitted light, for instance, by directing the light into a spectrometer. As a demonstration, we measured tip induced photoluminescence spectra of a gold surface. Furthermore, we demonstrate that we can simultaneously record scanning tunneling microscope induced luminescence and topography of the surface both with atomic resolution

Semiconductors studied by cross-sectional scanning tunneling microscopy

No abstract

High-field magnetotransport in a two-dimensional electron gas in quantizing magnetic fields and intense terahertz laser fields

We present a combined experimental and theoretical study of interactions between two-dimensional electron gases (2DEGs) and terahertz (THz) free-electron lasers in the presence of quantizing magnetic fields. It is found both experimentally and theoretically that when an intense THz field and a quantizing magnetic field are applied simultaneously to a GaAs-based 2DEG in the Faraday geometry, a strong cyclotron resonance (CR) effect on top of the magnetophonon resonances can be observed by transport measurements at relatively high temperatures. With increasing radiation intensity and/or decreasing temperature, the peaks of the CR are broadened and split due to magnetophoton-phonon scatterin

Tunable switching dynamics of a single Si dopant in GaAs(110)

The dynamic behavior of single bistable Si dopants in the GaAs (110) surface, which switch between a positive and a negative charge configuration, was investigated using a scanning tunneling icroscope (STM) and noise analysis electronics. The dopant atom switching frequency shows a clear dependence on the bias voltage and tunneling current, because these parameters influence the escape and capture processes of electrons. Our physical model for these processes, taking into account the relevant tunneling barriers, matches well with the experimental data. By choosing the appropriate tunneling conditions, we show that a single dopant can be employed as a memory element. The STM tip serves both as an electrical gate to write and as a probe to read the information stored on a single Si atom

Structural properties of Bi containing InP films explored by cross-sectional scanning

\u3cp\u3eThe structural properties of highly mismatched III-V semiconductors with small amounts of Bi are still not well understood at the atomic level. In this chapter, the potential of cross-sectional scanning tunneling microscopy (X-STM) to address these questions is reviewed. Special attention is paid to the X-STM contrast of isovalent impurities in the III-V system, which is discussed on the basis of theoretical STM images of the (110) surface using density functional theory (DFT) calculations. By comparing high-resolution X-STM images with complementary DFT calculations, Bi atoms down to the third monolayer below the InP (110) surface are identified. With this information, the Short-range ordering of Bi is studied, which reveals a strong tendency toward Bi pairing and clustering. In addition, the occurrence of Bi surface segregation at the interfaces of an InP/InP\u3csub\u3e1−x\u3c/sub\u3eBi\u3csub\u3ex\u3c/sub\u3e/InP quantum well with a Bi concentration of 2.4 % is discussed.\u3c/p\u3

Structural and electronic properties of isovalent boron atoms in GaAs

\u3cp\u3eBoron containing GaAs, which is grown by metal organic vapour phase epitaxy, is studied at the atomic level by cross-sectional scanning tunneling microscopy (X-STM) and spectroscopy (STS). In topographic X-STM images, three classes of B related features are identified, which are attributed to individual B atoms on substitutional Ga sites down to the second layer below the natural {110} cleavage planes. The X-STM contrast of B atoms below the surface reflects primarily the structural modification of the GaAs matrix by the small B atoms. However, B atoms in the cleavage plane have in contrast to conventional isovalent impurities, such as Al and In, a strong influence on the local electronic structure similar to donors or acceptors. STS measurements show that B in the GaAs {110} surfaces gives rise to a localized state short below the conduction band (CB) edge while in bulk GaAs, the B impurity state is resonant with the CB. The analysis of B\u3csub\u3ex\u3c/sub\u3eGa\u3csub\u3e1-\u3c/sub\u3e \u3csub\u3ex\u3c/sub\u3eAs/GaAs quantum wells reveals a good crystal quality and shows that the incorporation of B atoms in GaAs can be controlled along the [001] growth direction at the atomic level. Surprisingly, the formation of the first and fourth nearest neighbor B pairs, which are oriented along the 110 directions, is strongly suppressed at a B concentration of 1% while the third nearest neighbor B pairs are found more than twice as often than expected for a completely spatially random pattern.\u3c/p\u3

Random electric fields and impurity diffusion in δ layers

Impurity diffusion in the d layer during the process of its growth has been considered. Experiments show that the spreading of the impurity profile has a complex dependence on the in-plane impurity concentration. We carried out the numerical simulation of the self-consistent diffusion problem for the impurities moving in their own random electric field and have shown that at some critical impurity concentration in d layer the impurity distribution function perpendicular to the layer acquires a non-Gaussian character

Determination of the intra - and inter-subband scattering times in a degenerate dimensional electron gas

Measurements of magnetoresistance oscillations have been performed for a twodimensional electron gas where two subbands are occupied to study processes of inter- and intra-subband scattering. Analysis of the temperature dependence of the oscillations allowed us to estimate independently inter- and intra-subband scattering times in the subbands. It has been found that the mobility in the first subband is mainly determined by the intra-subband scattering events, while that in the second subband is limited by processes of inter-subband scattering

InAs quantum dot morphology after capping with In, N, Sb alloyed thin films

Using a thin capping layer to engineer the structural and optical properties of InAs/GaAs quantum dots (QDs) has become common practice in the last decade. Traditionally, the main parameter considered has been the strain in the QD/capping layer system. With the advent of more exotic alloys, it has become clear that other mechanisms significantly alter the QD size and shape as well. Larger bond strengths, surfactants, and phase separation are known to act on QD properties but are far from being fully understood. In this study, we investigate at the atomic scale the influence of these effects on the morphology of capped QDs with cross-sectional scanning tunneling microscopy. A broad range of capping materials (InGaAs, GaAsSb, GaAsN, InGaAsN, and GaAsSbN) are compared. The QD morphology is related to photoluminescence characteristics

Interplay between tip-induced band bending and voltage-dependent surface corrugation on GaAs(110) surfaces

Atomically resolved, voltage-dependent scanning tunneling microscopy (STM) images of GaAs(110) are compared to the results of a one-dimensional model used to calculate the amount of tip-induced band bending for a tunneling junction between a metal and a semiconductor. The voltage-dependent changes in the morphology of the atomic lattice are caused by the four surface states of the GaAs(110) surface contributing in varying relative amounts to the total tunneling current. Tip-induced band bending determines which of these states contributes to the total tunneling current at a given bias voltage, and thus has a profound influence on the voltage-dependent STM-images. It is shown that certain voltage regions exist, for which none of the surface states present at the GaAs(110) surface can contribute to the tunneling current. For these voltages, tunneling occurs between the tip and bulk states of the sample through a surface depletion layer several nm wide. Nevertheless, we observe atomic, surface like corrugation for these circumstance