HYDROGEN DIFFUSION IN A-SI-H/A-SI STRUCTURE UNDER ELECTRICAL BIAS

By using the technique of elastic recoil detection (ERD), we have measured the hydrogen profiles in a-Si:H/a-Si structure samples annealed at various temperatures with and without electrical bias, and investigated the influence of electrical bias on hydrogen diffusion. The results show that hydrogen diffusion in a-Si is significantly enhanced by the action of electrical bias. The existence of the excess carriers, which are introduced by electrical injection, is considered to be responsible for the enhancement of hydrogen diffusion, and the microprocess of hydrogen transport has been exploited.

STRUCTURAL DEFECTS AND THEIR ELECTRICAL-ACTIVITY IN GERMANIUM IMPLANTED SILICON

The electrical and structural characteristics of secondary defects in regrown amorphous layers formed in n-type Si(100) with a resistivity of 2 OMEGA cm and 6 OMEGA cm using Ge+ ions, has been studied. The amorphous layers with a thickness of 460 nm are formed by implantation of 1 x 10(15) Ge+ cm-2 at an energy of 400 keV. Both conventional furnace and rapid thermal annealing were used to regrow the amorphous layer and the residual defects have been characterised in terms of their concentration depth distribution and activation energies using C-V and DLTS. Structural information has been obtained from RBS and XTEM. By choosing suitable anneal conditions it is possible to eliminate extended defects, apart from a low concentration of end of range dislocation loops. However, a substantial population of electrically active point defects remain after simple low thermal budget anneals. In a sample implanted with 1 x 10(15) Ge+ cm-2 at 400 keV a region of deep donors approximately 460 nm from the surface is always present When the samples are annealed at higher temperatures (> 850-degrees the total deep donor concentration is reduced by one order of magnitude. Other electrically active defects not observable in the low (750-degrees-C) temperature annealed layers become apparent during anneals at intermediate temperatures.

ELECTRICAL CHARACTERS OF OXYGEN DEFECTS IN SILICON SUBJECTED TO INTRINSIC GETTERING TREATMENT

The influence of oxygen defects on the resistivity and mobility of silicon wafers is discussed. Grinding processes were performed on the surfaces of samples in order to obtain the information on interior defects of the samples. Spreading resistivity and Hall measurements prove that SiO(x) complexes alone result in resistivity increase and mobility decrease. Deep level transient spectroscopy experiments prove that SiO(x) complexes alone are electrically active. A mechanism of carrier scattering by electrically active SiO(x) complex is proposed to explain the changes of resistivity and mobility.

Correlation of electrical and optical properties in dually Cd+ and N+ ion-implanted GaAs

Cd in GaAs is an acceptor atom and has the largest atomic diameter among the four commonly-used group-II shallow acceptor impurities (Be, Mg, Zn and Cd). The activation energy of Cd (34.7 meV) is also the largest one in the above four impurities, When Cd is doped by ion implantation, the effects of lattice distortion are expected to be apparently different from those samples ion-implanted by acceptor impurities with smaller atomic diameter. In order to compensate the lattice expansion and simultaneously to adjust the crystal stoichiometry, dual incorporation of Cd and nitrogen (N) was carried out into GaAs, Ion implantation of Cd was made at room temperature, using three energies (400 keV, 210 keV, 110 keV) to establish a flat distribution, The spatial profile of N atoms was adjusted so as to match that of Cd ones, The concentration of Cd and N atoms, [Cd] and [N] varied between 1 x 10(16) cm(-3) and 1 x 10(20) cm(-3). Two type of samples, i.e., solely Cd+ ion-implanted and dually (Cd+ + N+) ion-implanted with [Cd] = [N] were prepared, For characterization, Hall effects and photoluminescence (PL) measurements were performed at room temperature and 2 K, respectively. Hall effects measurements revealed that for dually ion-implanted samples, the highest activation efficiency was similar to 40% for [Cd] (= [N])= 1 x 10(18) cm(-3). PL measurements indicated that [g-g] and [g-g](i) (i = 2, 3, alpha, beta,...), the emissions due to the multiple energy levels of acceptor-acceptor pairs are significantly suppressed by the incorporation of N atoms, For [Cd] = [N] greater than or equal to 1 x 10(19) cm(-3), a moderately deep emission denoted by (Cd, N) is formed at around 1.45-1.41 eV. PL measurements using a Ge detector indicated that (Cd, N) is increasingly red-shifted in energy and its intensity is enhanced with increasing [Cd] = [N], (Cd, N) becomes a dominant emission for [Cd] = [N] = 1 x 10(20) cm(-3). The steep reduction of net hole carrier concentration observed for [Cd]/[N] less than or equal to 1 was ascribed to the formation of (Cd, N) which is presumed to be a novel radiative complex center between acceptor and isoelectronic atoms in GaAs.

Quantum dot superlattices and their conductance

The one-dimensional energy bands and corresponding conductivities of a T-shaped quantum-dot superlattice are studied in various cases: different periods, with potential barriers between dots, and in transverse electric fields. It is found that the conductivity of the superlattices has a similar energy relation to the conductance of a single quantum dot, but vanishes in the energy gap region. The energy band of a superlattice with periodically modulated conducting width in the perpendicular magnetic field is calculated for comparison with magneto-transport experiments. It is found that due to the edge state effect the electron has strong quantum transport features. The energy gaps change with the width of the channel, corresponding to the deep peaks in the conductance curve. This method of calculating the energy bands of quantum-dot superlattices is applicable to complex geometric structures without substantial difficulty. (C) 1997 American Institute of Physics.

Electrical properties of semi-insulating GaAs grown from the melt under microgravity conditions

A technologically important undoped semi-insulating (SI) GaAs single crystal was successfully grown in the Chinese recoverable satellite as far as we know for the first time by using a similar growth configuration described previously. The experimental results proved that the space SI GaAs crystals have a lower density of defects and defect-impurity complexes as well as a better uniformity.

Investigation on the N-eff reverse annealing effect using TSC/I-DLTS: Relationship between neutron induced microscopic defects and silicon detector electrical degradations

Neutron induced defect levels in high resistivity silicon detectors have been studied using a current-based macroscopic defect analysis system: thermally stimulated current (TSC) and current deep level transient spectroscopy (I-DLTS). These studies have been correlated to the traditional C-V, I-V, and transient current and charge techniques (TCT/TChT) after neutron radiation and subsequent thermal anneals. It has been found that the increases of the space charge density, N-eff, in irradiated detectors after thermal anneals (N-eff reverse anneal) correspond to the increases of deep levels in the silicon bandgap. In particular, increases of the double vacancy center (V-V and V-V-- -) and/or C-i-O-i level have good correlations with the N-eff reverse anneal. It has also been observed that the leakage current of highly irradiated (Phi(n) > 10(13) n/cm(2)) detectors increases after thermal anneals, which is different from the leakage current annealing behavior of slightly irradiated (Phi(n) < 10(13) n/cm(2)) detectors. It is apparent that V-V center and/or C-i-O-i level play important roles in both N-eff and leakage current degradations for highly irradiated high resistivity silicon detectors.

A transfer matrix approach to conductance in quantum waveguides

A transfer matrix approach is presented for the study of electron conduction in an arbitrarily shaped cavity structure embedded in a quantum wire. Using the boundary conditions for wave functions, the transfer matrix at an interface with a discontinuous potential boundary is obtained for the first time. The total transfer matrix is calculated by multiplication of the transfer matrix for each segment of the structure as well as numerical integration of coupled second-order differential equations. The proposed method is applied to the evaluation of the conductance and the electron probability density in several typical cavity structures. The effect of the geometrical features on the electron transmission is discussed in detail. In the numerical calculations, the method is found to be more efficient than most of the other methods in the literature and the results are found to be in excellent agreement with those obtained by the recursive Green's function method.

Temperature dependence of the low-field mobility of a very narrow miniband in the degenerate case

Perpendicular transport in a specially designed, doped and weakly coupled GaAs/AlAs superlattice is investigated. A linear current-voltage at a bias within +/-10 mV and a negative differential velocity effect at a bias of about +/-40 mV are observed at low temperatures. The miniband conductance near zero electric field is studied as a function of temperature. It is found that the measured conductance increases slightly as the temperature increases to about 30 K, decreases as the temperature rises from 30 K to 70 K, and then increases strongly above 70 K, indicating the existence of a mobility gap.