Yasunori Mochizuki

Effects of thermal annealing on porous silicon photoluminescence dynamics

Photoluminescence (PL) spectra and decay dynamics were studied for the spontaneously oxidized porous Si with subsequent various thermal annealing procedures. The PL decay was highly nonexponential and well described by the stretched‐exponential function. The PL lifetime was shorter for the higher PL photon energy, but at the same photon energy it decreased by an order of magnitude by the thermal annealing in N2 gas, in parallel with the large PL intensity decrease. This PL quenching upon the annealing is presumably ascribable to both the structural changes and dangling bond formations in porous Si, as suggested by ESR measurements and the annealing experiments in H2 gas.

Precise control of pn-junction profiles for GaN-based LD structures using GaN substrates with low dislocation densities

Abstract Doping profiles of pn-junctions for GaN-based laser diode structures were studied using SIMS and EBIC measurements. Mg impurity, a p-type dopant, was found to diffuse heavily into the n-type region of the order of 10 17 xa0cm −3 when a sample is grown on a sapphire substrate. This unwanted diffusion appears closely related to the presence of threading dislocations, and can be eliminated by using high-quality GaN substrates for epitaxial growth.

Interface‐state density at SiO2/GaAs assessed by direct measurement of surface band bending

Electroreflectance is applied to study the interface properties of metal/SiO2/GaAs structures. From a bias‐voltage dependence of surface potential, which was evaluated from the measured surface field in i/n+‐GaAs structures, energy distributions of interface‐state density were determined based on the modulation spectroscopy technique. Upon biasing toward inversion, a strong pinning of surface Fermi level occurred at around 0.88 eV below the conduction‐band minimum. This pinning, thus, is concluded to be due to a large number of interface states, and not due to an actual hole inversion. The method is free from numerical ambiguities encountered in capacitance‐based techniques, in which the energy reference for surface Fermi level is model dependent, and thus, is a suitable tool for studying insulator/semiconductor interfaces, even having a large number of interface traps.

Role of dangling bond centers on radiative recombination processes in porous silicon

The role of Si dangling bonds (Pb center) on the broad luminescence band around 1.1 eV of porous Si is discussed, based on transient wave form measurement of optically detected magnetic resonance. The observed wave form is compatible with the nongeminate shunt path scheme and the characteristic time constant of this nonradiative process is deduced to be 15 μs at 1.6 K, whereas the competing radiative channel has a shorter decay time of 3 μs. Therefore, Pb centers are unlikely to be involved as a radiative state in this infrared luminescence. Results are also discussed in conjunction with the visible luminescence process.

Electrically detected magnetic resonance of ion-implantation damage centers in silicon large-scale integrated circuits

Two types of defects were detected in the source/drain ( n 1 -type! region of 0.25-mm-gate-length n-channel metal oxide semiconductor field-effect-transistors on LSIs: ~i! a spin-1 Si dangling-bond ~DB! pair in divacancy‐oxygen complexes ~DB‐DB distance, R’0.6 nm); and ~ii! a series of larger Si vacancies involving distant Si DBs ( R>1.4 nm). These vacancy-type defects were much more thermally stable in Si LSIs than those in bulk Si crystals. We suggested two physical mechanisms for this enhanced stability: internal mechanical stress and oxygen incorporation in the active regions of LSIs. After examining the relationship between the defects and current‐voltage characteristics, we concluded that these defects are distributed in the near-surface n 1 -type region close to the gate and that they are the source of the gate-induced drain leakage currents.

Hydrogen passivation of impurities in GaP as studied by photoluminescence spectroscopy

Hydrogen passivation of several types of impurities in GaP has been investigated by the use of low‐temperature photoluminescence, secondary ion mass spectrometry, and electrical measurements. Exposure to atomic hydrogen has completely arrested optical activity of acceptor Zn, as detected by photoluminescence, whereas those of donor S and isoelectronic impurity N have not changed. Neutralization of the Zn acceptor is reversible in the sense that the original activity can be restored by a low‐temperature anneal. These changes in luminescent activity are fully consistent with the results of electrical measurements and mass analysis.

Defects related to DRAM leakage current studied by electrically detected magnetic resonance

Abstract The defects responsible for the charge leak of dynamic random access memory (DRAM) memory cells were revealed by a novel type of electrically detected magnetic resonance measurements. The detection sensitivity was greatly improved by using reverse-biased p – n junctions, which enabled us to specify the defect structure. Two types of defects were identified as the origin of the leakage currents; the spin-1 Si dangling-bond (DB) pair in divacancy-oxygen complexes (V 2 +O and V 2 +O 2 ) or Si DBs of a different kind from the well-known Si DB center ( g =2.0055). It is notable that such defects remain in the device structure in spite of their low thermal stability in Si bulk.

Real-time electron-ion dynamics for photoinduced reactivation of hydrogen-passivated donors in GaAs

Photoassisted reactivation of H-passivated Si donors in GaAs has been demonstrated by first-principles calculations. In order to examine the survival of the excited state, we have applied our recently developed scheme of the ab initio molecular dynamics coupled with the time-dependent Schrodinger equation for electrons. We have found a possible electronic excitation which significantly lowers the dissociation-barrier height from 1.79 to 0.23 eV. This result explains well the recent experiment of carrier recovery by laser illumination [D. Loridant-Bernard, S. Meziere, M. Constant, N. Dupuy, B. Sombret, and J. Chevallier, Appl. Phys. Lett. 73, 644 (1998)].

Charge-trapping defects in Cat-CVD silicon nitride films

We show that Cat-CVD silicon nitride films contain more than 10 19 cm -3 nitrogen-bonded Si dangling bonds, similarly to the case for conventional CVD films. However, the charge-trapping behavior of the Cat-CVD films is found to be quite different, in spite of the same origin for the dominant defects. The difference is ascribed to a non-uniform distribution of defects that is strongly depleted near the surface in Cat-CVD films.

Electroreflectance investigation of trapping states at SiO2/GaAs interfaces

Abstract Electroreflectance spectroscopy is applied to evaluate energy distributions of interface-state densities in GaAs-based metal-insulator-semiconductor diodes. In this method, bias-voltage dependence of surface Fermi-level positions is obtained by directly measuring the magnitude of semiconductor surface electric fields via analysis of the Franz-Keldysh oscillation spectra. An enhanced accuracy is available through the use of undoped/n + -GaAs junction structures for the test diodes. The result indicates that movement of surface Fermi-level toward the valence band is pinned at E C − 0.88 eV, where a steep rise in the interface-state density was observed. The method is free from the uncertainties experienced in the conventional capacitance technique, when applied to trap-rich interfaces, and thus, is useful in elucidating interface-originated problems in GaAs-based devices.