M. Kučera

The metastability of porous silicon/crystalline silicon structure

Abstract This contribution presents several new experimental results provided by the techniques of X-ray diffraction at grazing incidence, photoluminescence at 6K, c Q -V and charge version of deep level transient spectroscopy on porous silicon (thickness ~ 1 μm)/crystalline silicon structures prepared by the standard electrochemical etching process. An existence of new XRGI distinct reflection at 2θ = 38.5 °, coming from the polycrystalline structure of the porous silicon layer, has been confirmed. For the first time we revealed a reversible metastability feature of two groups of gap states with the thermal activation energies of ~ 0.53 and ~ 0.70 eV, respectively. The metastable properties are related to the changes of both the water and hydrogen contents in the porous silicon layer induced by a low temperature annealing process.

The influence of the inductively-coupled hydrogen plasma on the GaAs surface properties

Abstract Properties of the high-doped GaAs crystalline surface regions exposed to the inductively coupled hydrogen plasma were investigated by photoluminescence, photoreflectance and X-ray diffraction (at grazing incidence) methods. The main results obtained lead to the conclusion that besides the apparent passivation effect the initial photoluminescence spectrum was totally transformed during the advanced stage of the hydrogenation process. We suppose that the defect complex corresponding to the ∼1.0 eV transition was transformed during the hydrogenation to another one with the 1.23 eV broad emission band. The rise of the new photoluminescence maximum at 1.44 eV and the extinction of that at 1.49 eV were observed. The X-ray measurements indicate that the thin outermost surface layer with the typical polycrystalline structure was also transformed.

Low-energy particle treatment of GaAs surface

Abstract Modification of high-doped GaAs surface by the interaction with RF plasma and a monoenergetic beam of similar chemical composition (Ar with a low content of H 2 ) was investigated via the evolution of optical, electrical and structural properties. A reduction in the free charge concentration in the GaAs surface region of ∼100 nm in thickness is concluded from Raman spectroscopy. In the processed samples, the surface electric field strength induced by a laser beam (photoreflectance technique) continually decreases with both the energy and fluence of impinging particles. The same results were obtained by evaluation of quasistatic C – V curves of corresponding MOS structures. They confirmed that longer exposure caused the formation of ∼100-nm-thick modified near-surface region with a decreased donor concentration. After the plasma irradiation, an ∼10-nm-thick outermost insulating layer was created in situ. The formation of textured polycrystalline grains with (100) orientation in the surface region was observed by X-ray diffraction.

Photoluminescence of passivated a-Si:H

. Experimental results relating to evolution of the a-Si:H photoluminescence spectra are presented. The investigated samples were prepared by deposition of thin a-Si:H layer on glass substrate. In the a-Si:H surface region very thin oxide layer was prepared by wet chemical oxidation in 40% nitric acid solution. The defect states of amorphous silicon layer and its interface with oxide were passivated in HCN aqueous solutions. The attention was focused on decomposition procedure of photoluminescence spectra observed at 6 K. The results confirm the existence of several structurally different phases inside of the a-Si:H amorphous matrix. PACS: 78.55.-m, 78.55.Qr, 81.05.Gc

Plasma anodic oxidation of semiinsulating GaAs

Abstract A technique is presented for the plasma anodic oxidation of semiinsulating (SI) GaAs surfaces at elevated sample temperatures (up to 230°C) the anodization current being fed vertically across the semiconductor. Capacitance and resistance measurements were performed on corresponding MOS structures for the determination of the lowest temperature at which the oxide growth can proceed. The oxide/SI-GaAs interface properties were investigated by correlation of DLTS, photoluminescence and X-ray reflectivity methods with the aim to better clarify the oxidation kinetics. Moreover, it was determined that the interface region seems to be better formed, being thinner, when a thin aluminium coverage layer is deposited on the SI-GaAs surface before the oxidation process. On the basis of our experimental results, we presume that each anodic oxidation process can be characterized by a cross section of the reaction of the oxygen ions with the semiconductor atoms due to the different oxidation state of the latter which is determined by given oxidation conditions. Its value for SI-GaAs sample at 230°C has been calculated to be ∼ 3.0 × 10 −14 cm 2 .

Regarding the Optical Properties of Porous Layers Prepared on Si Substrates

The paper deals with the complex refractive index and photoluminescence in the IR-VIS light region of two sample types (i) black p-type silicon (BSi) produced by the surface structure chemical transfer method using Pt catalytic mesh, and (ii) porous p-type silicon prepared by standard electrochemical etching. We present, compare, and discuss the values of the IR-VIS complex refractive index obtained by calculation using the Kramers-Kronig transformation and the photoluminescence properties thereof. The results indicate that differences between the optical properties of the BSi and the porous Si are given by (a) the oxidation procedure of BSi, (b) the thickness of the formed black and porous Si layer, and by (c) the porosity of both layer types. We assume that the photoluminescence signal generated by oxidized BSi structures can be mainly related to the quantum confinement effect, while the photoluminescence of the porous p-type Si is caused by the optical activity of the SiOxHy compounds covering its surface region.

Temperature dependence of photoluminescence peaks of porous silicon structures

Abstract Evaluation of photoluminescence spectra of porous silicon (PS) samples prepared by electrochemical etching is presented. The samples were measured at temperatures 30, 70 and 150 K. Peak parameters (energy, intensity and width) were calculated. The PL spectrum was approximated by a set of Gaussian peaks. Their parameters were fixed using fitting a procedure in which the optimal number of peeks included into the model was estimated using the residuum of the approximation. The weak thermal dependence of the spectra indicates the strong influence of active defects.

Physical Properties and Light-Related Applications of Black Silicon Structures

This contribution deals with the black silicon (BS) nanocrystalline specimens produced using the surface structure chemical transfer method (SSCT). This method can produce a nanocrystalline Si black color layer on c-Si with a thickness range of ~50 nm to ~300 nm via the contact of c-Si immersed in the chemical solution HF + H2O2 with a catalytic mesh. The photoluminescence properties are related to the formation of nanocrystals, the structural properties of which are similar to those formed on the back of a sawn Si wafer and the resulting splitting of large Si crystals. X-ray diffraction of the Si front and back sides confirms the dominant reflection of the 311 Si crystalline planes. We suppose that the formation of the black silicon over-layer is pre-determined by the crystalline defects induced by the applied sawing procedure, even though saw damage (defects introduced by the applied sawing procedure) is not necessary for the SSCT method. The formation of the pn type Si solar cell is presented, including black silicon over-layer and without antireflection coating, with efficiency of ~19.1%.

Low-energy argon ion beam treatment of a-Si:H/Si structure

Abstract The results of several surface-sensitive techniques applied to the investigation of ion beam-treated a-Si:H/crystalline silicon structures, such as deep-level transient spectroscopy (DLTS), photoluminescence at 6 K and room temperature, and X-ray diffraction at grazing incidence (XRDGI) are presented. Three important results follow from this contribution. (i) Two groups of gap states with thermal activation energies of 0.71 and 0.84 eV were identified and found to be sensitive to illumination, this property exhibiting metastable character; we suppose effects similar to those observed in the porous silicon/silicon and a-Si:H/silicon structures. (ii) Broader luminescence peaks were identified optically with the energies lying in the range of 0.7 to 0.95 eV, the most distinct one being at 0.85 eV. (iii) X-ray reflection at 2θ∼28° has been found as the reflection suitable for tracing the structural properties of a-Si:H layer.

X-ray photoemission and photoreflectance study of Au/ultrathin Si/n-GaAs Schottky contacts and hydrogen plasma treated semi-insulating GaAs surfaces

The paper presents room temperature photoreflectance measurements carried out on the Au/ultrathin Si/n-crystalline GaAs structure with the silicon interlayer thickness gradually changing from about 4-27 Angstrom prepared in situ under ultra-high-vacuum conditions. A continuous change of the phase shift of the corresponding photoreflectance signal of more than 180 degrees has been observed in the Eg-critical-point oscillation of GaAs depending on the Si interlayer thickness. The explanation of the effect is based on the composition changes of the Au/Si interface monitored by X-ray photoelectron spectroscopy. The photoreflectance results are compared to the photoreflectance signal phase changes observed on the semi-insulating GaAs surfaces exposed to the low-temperature hydrogen plasma