Yoshifumi Yamashita

Photo-Enhanced Activation of Hydrogen-Passivated Magnesium in P-Type GaN Films

We studied the effect of UV-light irradiation on annealing of as-grown Mg-doped GaN films by resistivity and Hall measurements. The annealing temperature where the resistivity reduction due to the electrical activation of hydrogen-passivated Mg occurred with the increase of hole density and the decrease of hole mobility, was reduced from 550 to 450°C by the irradiation of UV light with a peak wavelength around 350 nm. This suggests that electronic excitation reduces the thermal stability of Mg-H complexes in GaN.

Dislocation motion in semiconducting crystals under the influence of electronic perturbations

The radiation enhanced dislocation glide effect was confirmed in h-ZnO as well as in other semiconductors, which proved further the ubiquitous nature of this effect in semiconductors. Analysis of the radiation enhanced dislocation vibrations observed in the same h-ZnO led us to a tentative model that the effect is brought about by fluctuations of the charge state of point defects which exert electrostatic forces on the charged dislocations. The hydrogen-plasma enhanced dislocation glide was studied in Ge, SiGe and GaAs in addition to the previous reports on Si. The absence of the hydrogen effect in α-dislocations in n-GaAs and in thin films of SiGe is interpreted in terms of the soliton model, the essence of which is a strong binding between kinks and hydrogens.

Deep center related to hydrogen and carbon in p‐type silicon

We have found a hole trap related to hydrogen and carbon in p‐type crystalline silicon after hydrogen and deuterium injection by chemical etching and plasma exposure. It was found from deep‐level transient spectroscopy that this center is located at 0.33 eV above the valence band and shows no Poole–Frenkel effect in electric fields lower than 6×103 V/cm. The depth profiling technique using deep‐level transient spectroscopy indicated that this center is distributed over the range 1–7 μm from the surface with densities of 1011–1013 cm−3, depending on the hydrogenation method. On the other hand, secondary ions mass spectroscopy revealed that the majority of deuterium injected into silicon exists within a much shallower region less than 60 nm from the surface with higher densities of 1018–1020 cm−3. We have therefore concluded that the majority of injected hydrogen stays in the near‐surface region probably in the form of a molecule and larger clusters and only the minority diffuses into the bulk in an atomic ...

Electronically induced instability of a hydrogen-carbon complex in silicon and its dissociation mechanism

We studied, by deep-level transient spectroscopy (DLTS), the dissociation mechanism of a hydrogen-carbon (H-C) complex, which has a donor level at E c-0.15 eV and acts as an electron trap in crystalline silicon. On the basis of our results and a previously proposed atomic model of the H-C complex, in which the hydrogen atom resides inside a silicon-carbon bond, we have proposed the following dissociation mechanism. The complex is stable in the positive charge state, and to dissociate it needs a hydrogen jump with an activation energy of 1.3 eV to break the bond with carbon and silicon. The complex becomes neutral by capturing an electron from the conduction band or accepting an electron directly from the valence band under electronic excitation, and is consequently dissociated at an activation energy of 0.5 eV due to the loss of binding. Strong evidence for the existence of the negative charge state of hydrogen in crystalline silicon is also presented.

Photoluminescence of Er in strained Si on SiGe layer

We studied photoluminescence of Er in strained Si on a SiGe layer (Si:Er:O/SiGe) and unstrained Si on a Si layer (Si:Er:O/Si) grown by molecular beam epitaxy. Er-related photoluminescence was observed in both Si:Er:O/SiGe and Si:Er:O/Si samples. The peak intensity of Si:Er:O/SiGe at 1.54 μm was higher than that of Si:Er:O/Si. Moreover, the spectrum of strained Si (Si:Er:O/SiGe) was much broader than that of unstrained Si (Si:Er:O/Si). These differences between Si:Er:O/SiGe and Si:Er:O/Si suggest that the optical activation of Er can be enhanced by the presence of strain.

Structure and Stress-Induced Alignment of a Hydrogen-Carbon Complex in Silicon

We applied deep-level transient spectroscopy (DLTS) under uniaxial stress to study the structure and bonding nature of a hydrogen-carbon (H-C) complex in Si. The application of and compressive stresses split the DLTS peak into two as ratios of 1:3 and 2:2, respectively, which were the ratios of the low-temperature peak to the high-temperature peak. No splitting was observed under the stress. These results indicate the trigonal symmetry of the H-C complex and the anti-bonding nature of its electronic state. We observed a stress-induced alignment of the complex at 250K for 50 min under a stress of 1 GPa.

Effects of Hydrogen on Depth Profile of Resistivity of SiGe on Si Substrate

We report that the resistivity of SiGe films deposited on a B-doped Si substrate by solid-source molecular beam epitaxy (MBE) is reduced by postgrowth hydrogen treatment and the subsequent annealing. This effect was observed near a bevel surface finished by mechanical polishing. Therefore, the damaged surface layer played an important role in this effect. The same reduction in the resistivity of the SiGe films was also observed by intentional supplying hydrogen during film deposition. These phenomena indicate that hydrogen assists the electrical activation of boron.

Observation of Long Relaxation from Fe0(3d8) to Fe+(3d7) by Electron Spin Resonance Measurement

We studied the change in the 3d-shell configurations of Fe in B-doped Si under illumination by electron spin resonance (ESR) measurement. ESR signals originating from Fei+(3d7) and Fei0(3d8) were observed in Fe- and B-doped Si. The ESR signal of Fei+(3d7) disappeared and the signal intensity of Fei0(3d8) increased under illumination. These changes of the ESR signals under illumination were caused by the change in the charge state from Fei+(3d7) to Fei0(3d8) due to the capture of an electron. Subsequently, the process of recovery from Fei0(3d8) to Fei+(3d7) due to the capture of a hole was observed after the light was turned off. We found that the relaxation time from Fei0(3d8) to Fei+(3d7) was approximately 30 s at 8 K. This was much longer than the lifetime of a free hole.

Stress-Induced Level Shift of a Hydrogen–Carbon Complex in Silicon

We have studied the stress-induced shift of a deep level at Ec-0.15 eV due to a hydrogen-carbon complex in Si using deep-level transient spectroscopy (DLTS) under uniaxial compressive stress. Linear stress dependencies of the ionization energy of the above level were observed for five components of split DLTS peaks altogether for , and stresses. By subtracting the stress shifts of conduction band minima from the stress dependencies of ionization energy, the net stress shifts of the energy level were obtained. Two piezospectroscopic parameters, A1 and A2, were determined as approximately 4 and -9.5 meV/GPa, respectively. Considering a molecular-orbital schematic suggested here and throughout, we conclude that the stress-induced level shifts and the split pattern of DLTS peaks reflect the trigonal symmetry and antibonding character of the electronic state of the complex. These properties are completely consistent with the atomic configuration in which a hydrogen atom occupies the bond-centered site between Si and C atoms.

Annihilation of thermal double donors in silicon

We performed systematic experiments on the annihilation of six species of thermal double donors, or TDDs (TDD1–TDD6) under various conditions in both carbon-lean and carbon-rich Si crystals, by means of low-temperature infrared spectroscopy. We found that two kinds of TDD annihilation occurred in two different time regions. The first annihilation occurred typically within 1000 min at 500 °C, and is ascribed to the dissociation of oxygen clusters responsible for TDDs. We analyzed TDD annihilation on the basis of the model of successive dissociation of oxygen clusters, and obtained an activation energy of about 4 eV and a pre-exponential factor of the order of 1022 s−1, regardless of TDD species and carbon density. We discuss the origin of such a high activation energy and a large pre-exponential factor. The second annihilation occurred typically after 1000 min at 500 °C, and is ascribed to the neutralization of TDDs. The neutralization behavior strongly depends on the amount of carbon in the silicon crysta...