D. O. Filatov

Confocal Raman microscopy of self-assembled GeSi/Si(001) Islands

The method of confocal Raman microscopy is used for the first time to study the spatial distribution of elemental composition and elastic strains in self-assembled GexSi1 − x/Si(001) islands grown by the method of sublimation molecular-beam epitaxy in the GeH4 ambient. The lines related to vibrational modes Si-Si, Ge-Ge, and Si-Ge are identified in the Raman spectra measured in the regions with dimensions <100 nm on the surface of the samples. The spatial distribution of the Ge atomic fraction x in the GexSi1 − x alloy and of the elastic strain ɛ (averaged in depth over the island layer) have been calculated from the maps of the Raman shifts of the corresponding lines over the sample surface. The dependences of x and ɛ on the islands’ growth temperature and on the nominal thickness of the deposited Ge layer have been studied.

Photodiodes based on self-assembled GeSi/Si(001) nanoisland arrays grown by the combined sublimation molecular-beam epitaxy of silicon and vapor-phase epitaxy of germanium

We investigate the photosensitivity spectra of photodiodes based on Si p-i-n structures with single-layered and multilayer self-assembled GeSi/Si(001) nanoisland arrays in the i region, which are grown using a technique combining Si molecular-beam epitaxy and Ge vapor-phase epitaxy, in dependence on the temperature, diode bias, and GeSi nanoisland parameters. We show that the temperature and field dependences of the diode photosensitivity in the spectral range of the interband optical absorption in GeSi nanoislands are determined by the ratio between the rate of emission of photoexcited holes from the nanoislands and the rate of the recombination of excess carriers in them. We demonstrate the possibility of determination of the hole recombination lifetime in GeSi nanoislands from the temperature and field dependences of the photosensitivity.

Investigation of the local density of states in self-assembled GeSi/Si(001) nanoislands by combined scanning tunneling and atomic-force microscopy

The local density of states in self-assembled GeSi/Si(001) nanoislands is investigated for the first time by combined tunneling and atomic-force scanning microscopy. Current images and tunneling spectra of individual GeSi/Si(001) islands are obtained. These measurements yield the spatial and energy distributions of the local density of states in GeSi islands, respectively. The tunneling spectroscopy data demonstrate that uncapped Ge0.3Si0.7/Si(001) islands behave as type-I heterostructures.

Photoluminescence of GeSi/Si nanoclusters formed by sublimation molecular-beam epitaxy in GeH4 medium

The morphology and photoluminescence spectra of GeSi/Si(001) heterostructures with nanoclusters formed by sublimation molecular-beam epitaxy in GeH4 medium are investigated as functions of growth conditions. It is established that the clusters nucleate by the Stranski-Krastanow mechanism; however, the coalescence processes substantially affect their morphology during further growth. Doubling of photoluminescence lines in nanoclusters associated with the radiative recombination inside the clusters and the blue shift of lines with increasing growth time associated with the Si diffusion from substrate into the clusters are observed. The conditions of forming uniform nanocluster arrays emitting at room temperature are determined.

Study of Local Density of Electron States in InGaAs/GaAs Quantum Rings by Combined STM/AFM

The electronic structure of self-assembled InGaAs/GaAs(001) quantum rings grown by atmospheric pressure metal-organic vapor phase epitaxy has been investigated by combined scanning tunneling/atomic force microscopy (STM/AFM) in ultrahigh vacuum (UHV) for the first time. The current images and the tunnel spectra of contact of Pt-coated Si AFM probe to the quantum ring heterostructure surface revealing the spatial distribution of the local density of states and the electron size quantization spectra in the quantum rings have been obtained.

Photodetectors on the basis of Ge/Si(001) heterostructures grown by the hot-wire CVD technique

The fabrication of photodetectors for the wavelength range of communications λ = 1.3–1.55 µm on the basis of Ge/Si(001) heterostructures with thick (~0.5 µm) Ge layers grown by the hot-wire technique at reduced growth temperatures (350°C) is reported. The single-crystal Ga layers are distinguished by a low density of threading dislocations (~105 cm–2). The photodetectors exhibit a rather high quantum efficiency (~0.05 at λ = 1.5 µm and 300 K) at moderate reverse saturation current densities (~10–2 A cm–2). Thus, it is shown that the hot-wire technique offers promise for the formation of integrated photodetectors for the wavelength range of communications, especially in the case of limitations on the conditions of heat treatments.

Photoelectric properties of the GeSi/Si heterostructures with self-assembled nanoclusters grown by sublimation molecular beam epitaxy in a GeH4 medium

The photosensitivity (PS) spectra of the GeSi/Si(001) heterostructures with self-assembled nanoclusters grown by sublimation molecular beam epitaxy in a GeH4 medium have been studied by photo-emf spectroscopy at the semiconductor/electrolyte junction (PSE) and by photo-emf and photocurrent spectroscopy of Schottky barriers including the temperature dependence of the PS spectra in the temperature range of 10–300 K. The bands related to the phonon assisted and phonon-less interband of spatially indirect optical transitions in the GeSi nanoclusters have been observed in the PS spectra even at 300 K. The scatter effect of the GeSi nanoclusters in size and/or in composition on the PS spectrum’s edge shape has been theoretically considered. The emission theory of the photoexcited carriers from the quantum wells of the GeSi/Si nanoclusters built-in to a Schottky barrier (p-tn junction, semiconductor/electrolyte junction) has been developed.

Ballistic Hole Emission Spectroscopy of Self-Assembled GeSi/Si(001) Nanoislands

Ballistic hole emission microscopy/spectroscopy has been applied to study the electronic structure of the hole states in the self-assembled GeSi/Si(001) nanoislands. The ballistic hole emission microscopic images demonstrated the spots of increased collector current related to the ballistic electron tunnelling via the confined valence band states in the GeSi/Si(001) nanoislands. In the ballistic hole emission spectra of the Ge hut clusters the stepwise features attributed to the quantum confined hole states have been observed. The results of present study demonstrate the capabilities of the ballistic hole emission microscopy/spectroscopy in the characterization of the electronic structures of the valence band states in the GeSi/Si nanostructures.

Effect of Pulsed Gamma-Neutron Irradiation on the Photosensitivity of Si-Based Photodiodes with GeSi Nanoislands and Ge Epitaxial Layers

A comparative study of the effect of pulsed γ-neutron irradiation on the photosensitivity spectra of Si p–n photodiodes with active layers based on self-assembled GeSi nanoisland arrays and Ge epitaxial layers is performed. The irradiation of photodiodes with GeSi nanoislands is found to not lead to photosensitivity degradation in the spectral region of interband optical absorption in nanoislands (wavelength range of 1.1–1.7 μm). At the same time, a steady decrease in the intrinsic photosensitivity of Si and the photosensitivity of photodiodes based on Ge epitaxial layers with an increase in irradiation dose is observed. This effect is attributed to the accumulation of radiation-induced defects in the Si matrix and deep in Ge epitaxial layers, respectively.

A random telegraph signal in tunneling silicon p–n junctions with GeSi nanoislands

We have experimentally discovered random telegraph signal generation in tunneling silicon p+–n+ junctions with embedded self-assembled GeSi nanoislands. The observed phenomenon is related to blocking of the electron tunneling via individual GeSi nanoislands due to the generation of holes in, and their thermal emission from, the nanoislands.