E. B. Yakimov

Spatial variations of doping and lifetime in epitaxial laterally overgrown GaN

Spatial variations of donor concentration and diffusion length/lifetime were studied for epitaxial laterally overgrown undoped n-GaN samples by electron beam induced current (EBIC) and microcathodoluminescence (MCL). The dependence of the EBIC signal collection efficiency on the probing beam accelerating voltage shows that the local electron concentration is three times lower and the local lifetime about twice as high in the laterally overgrown regions compared to the regions grown in the SiO2 mask windows. Band edge MCL profiling shows that the lifetime difference could be an order of magnitude higher. EBIC scans along the SiO2 stripes in the low dislocation density overgrown regions show long propagation distances of holes in the quasineutral part of the structure, explained by the existence of a potential profile forming a trough for transport of holes while spatially separating nonequilibrium carriers.Spatial variations of donor concentration and diffusion length/lifetime were studied for epitaxial laterally overgrown undoped n-GaN samples by electron beam induced current (EBIC) and microcathodoluminescence (MCL). The dependence of the EBIC signal collection efficiency on the probing beam accelerating voltage shows that the local electron concentration is three times lower and the local lifetime about twice as high in the laterally overgrown regions compared to the regions grown in the SiO2 mask windows. Band edge MCL profiling shows that the lifetime difference could be an order of magnitude higher. EBIC scans along the SiO2 stripes in the low dislocation density overgrown regions show long propagation distances of holes in the quasineutral part of the structure, explained by the existence of a potential profile forming a trough for transport of holes while spatially separating nonequilibrium carriers.

Effects of laterally overgrown n-GaN thickness on defect and deep level concentrations

The effects of the layer thickness and of Si doping on the dislocation type and density, electron concentration, and deep trap spectra were studied for epitaxially laterally overgrown (ELOG) GaN films with the ELOG region thickness varying from 6to12μm. Electron beam induced current imaging shows that for the thickest layers, the major part of the threading dislocations are filtered out while for thinner films they bend, but do not go out of play. The concentration of residual donors and major electron traps is found to decrease with increasing the film thickness. Si doping suppresses the concentration of the main electron trap with activation energy of 0.6eV and enhances the concentration of the main hole trap at Ev+0.85eV.

Donor nonuniformity in undoped and Si doped n-GaN prepared by epitaxial lateral overgrowth

Local donor concentrations were measured in the regions of lateral overgrowth and in the normal vertical growth regions of n-GaN films prepared by epitaxial lateral overgrowth (ELOG). The films were doped with Si to various concentrations. The local donor densities were determined from measurements of the collection efficiency dependence of the electron beam induced current (EBIC) on the energy of the probing electron beam. This dependence was compared with the results of theoretical modeling using the local donor density and diffusion length of charge carriers as fitting parameters. The results show that the donor concentration in the ELOG regions is systematically more than two times lower than the concentration in the vertical growth regions in the gaps of the SiO2 mask used for selective growth. The observed difference is ascribed to the anisotropy of the Si incorporation efficiency. Comparison of these EBIC results with the results of capacitance-voltage profiling obtained on large area Schottky diod...

EBIC measurements of small diffusion length in semiconductor structures

The problems arising under submicron diffusion-length measurements by EBIC are discussed. As an example, the results of diffusion-length measurements in GaN are presented. It is shown that fitting the collection efficiency dependence on beam energy is the most reliable method for this purpose. The depth-dose dependence for GaN is calculated by the Monte-Carlo method and its analytical approximation is presented. This expression was verified experimentally by simultaneous fitting of the collected current dependence on beam energy for a few applied bias values.

Temperature dependence of dislocation efficiency as sinks for self‐interstitials in silicon as measured by gold diffusion

The substitutional gold concentration introduced in silicon by a diffusion step between 850 and 1000 °C was measured by deep level transient spectroscopy both in floating zone (FZ) and Czochralski (Cz) silicon containing different dislocation densities. The comparison, in the same sample, of dislocated and undislocated regions allows the efficiency of dislocations as sinks for self‐interstitials γ to be measured as a function of diffusion temperature. In FZ silicon γ was found independent of temperature whereas in Cz silicon a remarkable temperature dependence for γ was observed which can be attributed to the release of dislocations by a thermally stimulated climbing mechanism from obstacles (i.e., oxygen segregation or precipitation).

High-resolution electron-beam-induced-current study of the defect structure in GaN epilayers

Electron-beam-induced-current (EBIC) investigations of GaN structures grown by metal–organic chemical vapour deposition on (0001) sapphire substrates have been carried out. It is shown that the widths of the EBIC profiles for individual extended defects can be as small as about 100 nm. This width is observed to decrease with decreasing diffusion length and/or with increasing electron beam energy. The high spatial resolution is explained by the small diffusion length in the samples under study. The diffusion length is small even in structures with dislocation densities of about 108 cm−3 and carrier mobilities of about 600 cm2 V−1 s−1 at 300 K and 1800 cm2 V−1 s−1 at 125 K.

Trapping of gold by nanocavities induced by H+ or He++ implantation in float zone and Czochralski grown silicon wafers

In silicon, implantation of He++ or H+ ions and subsequent annealing can lead to the formation of nanocavities below the implanted surface of the wafers. These nanocavities, which behave as trapping sites for metallic impurities, can be located near the devices in integrated circuits in order to induce a proximity gettering. In this article, we investigate, in float zone (FZ) and Czochralski (Cz) wafers, the trapping of gold by nanocavities formed by implantation of He++ or H+ ions at 250 keV and at a dose of 3×1016 cm−2 followed by subsequent annealing(s) at 750  °C for 1 h. Deep level transient spectroscopy profiles show that substitutional gold concentration decreases near the cavity band in FZ and Cz samples. Gold profiles obtained by secondary ion mass spectroscopy show that there is a strong trapping of gold in the cavity band in all samples. In the case of He++ implanted wafers, this trapping also occurs in the region between the implanted surface and the cavities, and the higher the oxygen concent...

Electrical, luminescent, and deep trap properties of Si doped n-GaN grown by pendeo epitaxy

Electrical and luminescent properties and deep trap spectra of Si doped GaN films grown by maskless epitaxial lateral overgrowth (MELO) are reported. The dislocation density in the wing region of the structure was 106 cm−2, while in the seed region it was 108 cm−2. The major electron traps present had activation energy of 0.56 eV and concentrations in the high 1015 cm−3 range. A comparison of diffusion length values and 0.56 eV trap concentration in MELO GaN and epitaxial lateral overgrowth (ELOG) GaN showed a good correlation, suggesting these traps could be effective in carrier recombination. The doped MELO films were more uniform in their electrical properties than either ELOG films or undoped MELO films. We also discuss the differences in deep trap spectra and luminescence spectra of low-dislocation-density MELO, ELOG, and bulk n-GaN samples grown by hydride vapor phase epitaxy. It is suggested that the observed differences could be caused by the differences in oxygen and carbon contamination levels.

Temperature dependence of electron beam induced current contrast of deformation-induced defects in silicon

Electron beam induced current (EBIC) investigations of plastically deformed silicon in the temperature range from 90 K to 300 K were carried out. It is found that the dislocation trails left behind moving dislocations are the main defects revealed by the EBIC in crystals deformed in clean conditions. With an increase of the contamination level, the dislocation contrast in p-type samples increases. It is observed that the EBIC contrasts of both dislocations and dislocation trails increase with cooling in p-type silicon, while in n-type samples the EBIC contrasts exhibit the opposite trends for both defects.

Studies of deep level centers determining the diffusion length in epitaxial layers and crystals of undoped n-GaN

A wide variety of parameters were measured for undoped n-GaN grown by hydride vapor phase epitaxy and compared to n-GaN films grown by conventional and lateral overgrowth metalorganic chemical vapor deposition. The parameters included deep level electron and hole trap spectra, microcathodoluminescence, electron beam induced current, diffusion length, and electron capture cross section from the dependence of the low temperature persistent photocapacitance on forward bias injection pulse duration. The results show a prominent role of electron traps with levels near Ec-0.56 eV in limiting the lifetime and diffusion length values in all these materials.