We have investigated the intrinsic defects in ZnO films grown by molecular beam epitaxy by annealing them in O2 and N2 atmosphere. We found that there is a good correlation between the annealing condition and photoluminescence characteristics. The results of annealing experiments suggest that the photoluminescence at 3.358 eV is caused by the excitons bound to oxygen vacancies. The green-yellow emission at around 2.3 eV is also observed in as-grown ZnO epitaxitial films. This emission becomes weak and the electron concentration increases when ZnO films are annealed in O2 atmosphere at 1000°C or in N2 atmosphere at 700°C. Since the donor in undoped ZnO is related to the oxygen vacancy, the observed green-yellow emission at around 2.3 eV is probably caused by defects other than oxygen vacancies. Our experimental results imply that it is related to interstitial Zn.

Epitaxial ZnO films have been grown on Si(111) substrates by molecular beam epitaxy using oxygen plasma. An initial Zn layer deposition followed by its oxidation produces a superior template for the subsequent ZnO growth and a low-temperature ZnO buffer layer improves the structural and optical properties of ZnO films. As a result, we succeeded in growing highquality ZnO films directly on Si substrates. We observed cracks composed of straight lines along the principal axes of the Si(111) surface. These cracks are probably caused by the difference in thermal expansion coefficient between ZnO and Si. X-ray diffraction measurements reveal that ZnO films do not include a rotational domain and the full width at half maximum of the diffraction peak of ZnO(0002) is 0.23 deg. The linewidth of the neutral-donor-bound exciton emission at 3.365 eV is as small as 6 meV at 10 K.

Epitaxial ZnO films have been grown on Si (111) substrates by molecular beam epitaxy using ozone as an oxygen source. An initial deposition of a Zn layer followed by its oxidation produces a superior template for the subsequent ZnO growth. The reflection high-energy electron diffraction measurement suggests that the initial Zn layer and ZnO film are rotated by 30 with respect to the Si substrate orientation. The X-ray diffraction measurement reveals that the as-grown ZnO films are strongly coriented and include no rotational domains. Although there exists a small trace of ZnO (10 1 11) domains, it easily disappears upon annealing at 1100 C for 1 min after growth. Low-temperature photoluminescence measurements indicate that the emission property is improved significantly after annealing. The bound-exciton emission at 3.354 eV is dominant and its fullwidth at half maximum is as small as 11 meV.

For the prediction of abnormal etching profiles, an ion trajectory prediction system has recently been developed. In this system, sheath modeling was combined with the on-wafer monitoring technique for accurate prediction. This system revealed that sidewall conductivity strongly affects the charge accumulation and ion trajectory in high-aspect-ratio holes. It was also found that the accumulated charge in adjacent holes is one of the reasons for the generation of twisting profiles according to analysis using the system. We presume that the prediction system is an effective tool for developing nanoscale fabrication.

Over 1.3 μ m continuous-wave laser emission from InGaSb quantum-dot laser diode fabricated on GaAs substrates Appl.