Cross-sectional scanning tunneling spectroscopy of cleaved, silicon-based metal–oxide–semiconductor junctions

The composition and strain relaxation of GaSb quantum dots grown by organometalic vapor phase deposition (OMVPE) on GaAs (001), is investigated by transmission electron microscopy (TEM) and atomic force microscopy (AFM) techniques. Similar to reports in previous publications [1][2], OMVPE growth of GaSb on GaAs occurs initially via the formation of a uniform 2D wetting layer. At some thickness, islands nucleate randomly and grow via mass transport from the wetting layer. The initial islands are coherently strained with round or elliptical shapes but eventually relax via the formation of edge dislocations (in-plane, 90° burgers vectors). Questions remain as to the degree of incorporation of As into the dots as a function of the growth conditions, and to the exact mechanism of the strain relaxation process.We find that the deposition of GaSb at 520C, V:III ratio of 2.5, to a thickness exceeding 2 monolayers (ML) results in the spontaneous assembly of GaSb islands. TEM plan-view images, FIG. 1, show islands with a density of 70 µm -2 and a rectangular morphology, always with the [110] direction elongated. These islands have relaxed as seen from the square network of misfit dislocations . FIG 1 (a) shows a dark field image with g = [220] that identify the burger's vector of the misfit dislocations to be the expected 90° edge type. FIG. 1 (b) shows a magnified image of a cluster of these islands taken under g = [004] 2-beam conditions. The misfit dislocations aligned with <110> directions are clearly distinguishable from translational Moiré fringes along [001]. The island shapes and densities observed by TEM are comparable to those observed by AFM (FIG.2), which also shows that the island heights grow from 5 to 10 nm with increasing GaSb growth time.The edge dislocations in FIG. 1 (b) occur with a 6.25 nm interspacing whereas the (004) Moiré fringes have a spacing of 2.12 nm. This Moiré fringe spacing indicates that the dot composition is GaSb (with little or no As). However, complete relaxation of a GaSb/GaAs interface (7.8% mismatch) by the formation of a/2[110] edge dislocations would mean a dislocation spacing of 5.2 nm smaller than the observed 6.25 nm. The results suggest that the dot composition is graded from 12% As at the interface decreasing to 100% Sb at the surface.This rectangular morphology indicates that the growth is not occurring at the same rate in each <110> direction. The ratio of the length to width of the islands ranges from 2 -5. This is either due to a difference in the surface diffusion of atoms to the island or due to differences in the rate of formation of the edge dislocations as the island exceeds a certain size in each direction. Studies of the effects of GaSb p-type doping on the island morphology will be described. [3] References [1] P.M. Thibado, B. R. Bennett, M. E. Twigg, et. al., J.

show abstract

“…

…”

supporting

confidence: 83%

Evolution of GaSb/GaAs Quantum Dot Strain Relaxation

et al. 2002

View full text Add to dashboard Cite

show abstract

“…Silver et al 1995, Thibado et al 1996. However, these are much easier to deal with than an a-Si:H PV cell, and our efforts have been directed towards overcoming the differences.…”

Section: Apparatus For Cross-sectioned Pv Cell Diagnosismentioning

confidence: 99%

“…Silver et al 1995, Smith et al 1995, Thibado et al 1996. However, there are several factors that make this much harder for a-Si:H PV cells.…”

Section: Introductionmentioning

confidence: 99%

Atomic-scale characterization of hydrogenated amorphous-silicon films and devices. Annual subcontract report, 14 February 1995--14 April 1996

Gallagher¹,

Barzen²,

Childs³

et al. 1997

View full text Add to dashboard Cite

“…As a probe is scanned over a specific area, the carrier density profile [6], the potential across abrupt junctions [7], the impurity distribution [8], and the carrier scattering near defect centers [9] can be measured at the same time. The carrier density of a semiconductor can be mapped by the capacitance-voltage (C-V ) dependence, and the geometrical structure can be measured by STM or AFM.…”

mentioning

confidence: 99%

Recombination dynamics of traps in SiO 2 layer on Si by scanning capacitance microscopy

Kang

Kim

Kuk

et al. 1998

Applied Physics A: Materials Science & Processing

View full text Add to dashboard Cite

The depth-dependent carrier density and trapped charges in an arsenic-implanted silicon sample were measured by using scanning capacitance microscopy (SCM). The position-dependent capacitance versus voltage scans were measured at various dc bias voltages. A strong dc bias dependence was observed at the interface of an abrupt junction between n + and p. The bias-dependent SCM images were used to follow the recombination dynamics of traps. The results show good agreement with quasi-three-dimensional simulations, suggesting that they can be used to map device structure.With the recent developments in silicon submicrometer technology, the characterization of the three-dimensional carrier density profile in a device has become one of the most important issues. In a sub-micron device, it is very difficult to directly measure the carrier density profile around the gate because many tools measure only the profile averaged over a large area. Secondary ion mass spectrometry (SIMS) and spreading resistance profilometry (SRP) have widely been used to measure dopant profiles. The tomographic approach [1] and the angle lapping technique [2] have been developed to measure two-dimensional profiles with improved resolution. Recently, nano-SRP, utilizing scanning probe microscopy, has further improved spatial resolution [3][4][5]. Other important problems in submicron MOS devices are device failure and noise from hot electron effects and trapped charges. If the gate oxide in a MOS device becomes thinner than 10 nm and 5 V is still applied to the gate, problems related to the hot electron effect and trapped charges become more serious. At present there is no tool to measure the local defects such as trapped charges and the defects created by hot electrons. When data is taken by macroscopic measuring tools and then compared with the simulated results poor agreement is found.Since the advent of the scanning tunneling microscope (STM) and the atomic force microscope (AFM), geometrical and electrical measurements of a semiconductor surface have become possible with atomic resolution. As a probe is scanned over a specific area, the carrier density profile [6], the potential across abrupt junctions [7], the impurity distribution [8], and the carrier scattering near defect centers [9] can be measured at the same time. The carrier density of a semiconductor can be mapped by the capacitance-voltage (C-V ) dependence, and the geometrical structure can be measured by STM or AFM. In order to have good spatial resolution, the sensitivity of the detector has to be better than 10 −19 F [10]. This can be achieved with the scanning capacitance microscope (SCM) operating under ambient conditions by using a sample with only a capping oxide and without any further extensive sample preparation. However, it only measures the carrier density rather than the dopant concentration of the semiconductor surface. If the dopant density does not vary abruptly within a few Debye lengths, it can be estimated from the measured C-V dependence [11]. In an earlier SCM...

show abstract

Cross-sectional scanning tunneling spectroscopy of cleaved, silicon-based metal–oxide–semiconductor junctions

Cited by 8 publications

References 8 publications

Evolution of GaSb/GaAs Quantum Dot Strain Relaxation

Evolution of GaSb/GaAs Quantum Dot Strain Relaxation

Atomic-scale characterization of hydrogenated amorphous-silicon films and devices. Annual subcontract report, 14 February 1995--14 April 1996

Recombination dynamics of traps in SiO 2 layer on Si by scanning capacitance microscopy

Contact Info

Product

Resources

About