Emil Pinčík

Current-voltage characteristics and charge DLTS spectra of proton-bombarded Schottky diodes on semi-insulating GaAs

Changes in the current-voltage characteristics and charge DLTS spectra of Schottky diodes on semi-insulating GaAs after irradiation by protons at different energies and doses are presented and discussed. Apart from a progressive degradation of the Schottky barriers with enhanced proton energy and dose, there is a threshold, positioned between 1014 and 1015protonscm2, for observing trap-limited transients.

New experimental facts on the Staebler–Wronski effect

Abstract The affect of light soaking on the gap-state distribution of undoped hydrogenated amorphous silicon (a-Si:H) has been investigated using the charge deep level transient spectroscopy (DLTS) technique. Measured spectra directly show the change in all the gap states (Dh, Dz, De) due to the prolonged illumination with low intensity white light. Results are tentatively interpreted evoking the pecularities of hydrogen diffusion in silicon.

Passivation of shallow donors in GaAs by oxygen plasma exposure

Heavily doped (ND ≈ 1018 cm-3) GaAs substrates were exposed to an inductively coupled plasma in the temperature region 110–140°C. Formation of a thin GaAs plasma oxide layer is accompanied by a substantial reduction of the electrical activity of shallow Si donors, which finding could be supported by a series of capacitance versus bias measurements. As revealed by related deep-level transient spectroscopy (DLTS) data on Al-plasma oxide-GaAs diodes, the currently observed U-shaped continuous energy distribution of interface states is in fact composed of essentially two distinct branches. The occurence of either of the branches is controlled predominantly by the oxygen partial pressure. A true accumulation of electrons at forward biases is impeded by the highly resistive intermediate layer between the undisturbed GaAs substrate and the plasma oxide. A possible role of hydrogen present in the discharge is discussed with regard to the annealing kinetics of passivated donors. A stable GaAs isolation and an almost defect-free GaAs/oxide interface can be reached by selecting an optimum oxygen pressure.

Properties of semiconductor surfaces covered with very thin insulating overlayers prepared by impacts of low-energy particles

This paper deals with the formation of very thin insulating layers on crystalline (GaAs) and amorphous semiconductors (a-Si:H and a-SiGe:H) prepared by the impacts of particles of a very low energy. Plasma, ion beams and plasma immersion ion implantation (PIII) as the sources of impacting particles were used and compared. The last technique was applied successfully for the first time in the case of amorphous silicon-based semiconductors. More diagnostics techniques were used for the investigation of the transformation of the semiconductor surface properties. In the a-Si:H based MOS structures prepared by PIII technology, only two groups of defects 0.82 and 1.25 eV (D(z) and D(e), respectively) were found. We suppose that the PIII technology using the implantation at the sample voltage of ca. -1000V causes the formation of a-Si:H layers with missing group of D(h) states. The only decisive parameter determining the formation of two groups of states is the negative potential of the sample during the implantation. In aSiGe:H based MOS structures, three distributions could be prepared by a bias annealing procedure: 0.47, 0.58 and 0.95 eV corresponding to p-type (D(h)) intrinsic (D(z)) and n-type (D(e)) distributions, respectively.

Study of density of interface states in MOS structure with ultrathin NAOS oxide

The quality of the interface region in a semiconductor device and the density of interface states (DOS) play important roles and become critical for the quality of the whole device containing ultrathin oxide films. In the present study the metal-oxide-semiconductor (MOS) structures with ultrathin SiO2 layer were prepared on Si(100) substrates by using a low temperature nitric acid oxidation of silicon (NAOS) method. Carrier confinement in the structure produces the space quantization effect important for localization of carriers in the structure and determination of the capacitance. We determined the DOS by using the theoretical capacitance of the MOS structure computed by the quantum mechanical approach. The development of the density of SiO2/Si interface states was analyzed by theoretical modeling of the C-V curves, based on the superposition of theoretical capacitance without interface states and additional capacitance corresponding to the charges trapped by the interface states. The development of the DOS distribution with the passivation procedures can be determined by this method.

Photoluminescence properties of a-Si:H based thin films and corresponding solar cells

Abstract Amorphous hydrogenated silicon (a-Si:H) is a well-known semiconductor with metastable properties. Direct surface exposure, as it occurs e.g. in rf plasma equipments, introduces damage due to the charged particle bombardment. The paper deals with photoluminiscence properties of virgin, oxide layer covered and chemically treated (in KCN solutions) surfaces of a-Si:H and corresponding solar cell structures. The cyanide treatment improves the electrical characteristics of MOS structures as well as solar cells. X-ray diffraction at grazing incidence and reflectance spectroscopy complete the study. The photoluminescence measurements were performed at liquid helium temperatures at 6 K using an Ar laser and lock-in signal recording device containing the PbS and Ge photodetectors. Photoluminescence bands were observed as broad luminescent peaks between 1.05–1.7 eV. Two new peaks were detected at 1.38 and 1.42 eV. The evolution of the band at ∼1.2 eV related to microcrystalline silicon is investigated. The fitting and simulation of photoluminiscence spectra are presented. The surface luminescent properties of a-Si:H based structures (double layers, single thin film solar cells) before and after the passivation are compared with those of very thin oxide layers and chemically treated surfaces.

Defect re-distribution in amorphous silicon below equilibration temperature

Abstract The effect of a Fermi level shift in an intrinsic energy distribution of gap states of amorphous silicon prepared by glow discharge is investigated with the aim of simulating the energy distribution of gap states near the i–n (p–i) interface in a p–i–n (n–i–p) device. Therefore we carried out experiments in which the Fermi level is moved to either the conduction or valence band edge in a ‘programmed’ intrinsic energy distribution of gap states by subjecting a metal/insulator/amorphous-silicon structure to n-type or p-type bias stress, respectively. Its effect on the energy distribution of gap states is measured by the charge version of deep level transient spectrometry. We observe that upon n-type (p-type) bias stress the energy distribution of gap states does not immediately adjust to the applied Fermi level shift, but that first an intermediate distribution is formed with a larger neutral dangling bond state contribution. In addition, it appears that the negatively charged dangling bond states are more resistant to p-type stress than the positively charged dangling bond to n-type stress.

On Topographic Properties of Semiconductor Surfaces and Thin Film Systems

The microroughness of the semiconductor/oxide interface substantially influence properties of the whole structure. In our work Si/SiO2/SiOx structures were prepared by using low temperature nitric acid oxidation technique and by the electron gun technique and then the whole structure was passivated by the HCN technique. In the present study we investigate the surface morphology evolution during the creation of the SiO2/SiOx double-layer and after the passivation steps. Surface roughness properties are studied by the fractal geometry methods. The complexity of analysed surface is sensitive to the oxidation and passivation steps and the proposed fractal complexity measure values enable quantifying of the fine surface changes.

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.

Proton Implantation Induced Damage to Heavily Doped n‐GaAs as Envisaged by Charge Deep‐Level Transient Spectroscopy

Heavily doped (1 to 3 x 10 18 cm -3 ) GaAs:Si wafers were exposed to high doses (10 14 , 10 15 cm -2 ) of 150 keV protons. When applying the lower dose, the related charge DLTS spectra of Al/GaAs diodes comprise a peak of dielectric relaxation (DR) and a trap-limited peak (MG) due to the emission from a midgap level. The former peak can be attributed to a linear Debye-type polarization connected with a hopping transport of electrons within the damaged region. If taking samples from different positions on the original wafer, the position of the DR peak on the temperature axis T m , for a selected rate window has been found to vary when passing from one sample to another, a shift toward higher temperature has been accompanied by a corresponding increase in the activation energy (0.1 to 0.22 eV). The MG level emission rate is quite sensitive to the electric field intensity in the semiconductor, as manifested by shifting T m to lower temperatures via higher reverse biases. By contrast, the ultimate dose of 10 15 protons/cm 2 introduced defect levels at 0.07 and 0.31 eV below E c , respectively, a result that can be reconciled with previous reports relevant to lower doses. Concluding, the DR peak occurrence may be considered as a criterion for a successful GaAs isolation after the impact of protons, the optimum dose lying closely to the 10 14 cm -2 level.