Masahiko Kitagawa

Homoepitaxial growth of ZnS single crystal thin films by molecular beam epitaxy

Abstract Homoepitaxial ZnS single crystal films have been grown on ZnS(100) substrates at a low temperature of 260°C by molecular beam epitaxy using a high-temperature S beam heated up at 800°C. Crystallinity, surface morphology and growth rate of the films grown under various beam conditions (Zn beam pressure P Zn =(0.1−1.8) x 10 -6 Torr, S beam pressure P S =(1.6−3.7) x 10 -6 Torr and beam pressure ratio P S / P Zn =1–32) were investigated. Under the above beam conditions, the growth rate was independent of P Zn , proportional to the square of P S , and was higher on (100)4°–5° off substrates than on (100) substrates. From these results, the growth kinetics were presumed to be governed by a pairwise interaction of S molecules with a Zn atom at a step site on the growth surface. ZnS single crystal films with good crystallinity and flat surfaces were successfully grown at high beam pressure ratios ( P S / P Zn > 4). On the other hand, crystallinity and surface morphology of the grown films became worse on decreasing the beam pressure ratio ( P S / P Zn

Photo-assisted homoepitaxial growth of ZnS by molecular beam epitaxy

Abstract A novel thin film growth technique, photo-assisted homoepitaxy of ZnS usingmolecular beam epitaxy (MBE), has been carried out with elemental zinc (Zn) and elemental sulphur (S) as source materials. The crystallinity of ZnS was greatly improved by irradiation with 350 nm monochromated ultraviolet light from a xenon lamp. The growth rate was about 0.6 μm/h at 260°C. The crystal quality was characterized by RHEED patterns, surface photographs and photoluminescence spectra. Finally, the irradiation intensity dependence and the growth mechanism were discussed.

Homoepitaxial growth of low-resistivity-Al-doped ZnS single crystal films by molecular beam epitaxy

Abstract Low-resistivity-Al-doped ZnS homoepitaxial films have been grown by molecular beam epitaxy. The lowest resistivity of 2.2×10 -3 Ω cm was obtained at an Al concentration of 4.6×10 19 cm -3 in the ZnS(100) single crystal films grown at 260°C. Th e electron concentration was 3.9×10 19 cm -3 . Films with Al concentrations between 10 18 and 10 19 cm -3 showed excellent photolumi nescence spectra which exhibit strong and dominant near-band-edge emission of 3.785 eV at 77 K.

Dependence of device characteristics on quantum well thickness in ZnSe/ZnCdSe multi-quantum well blue-green laser diodes

Abstract ZnSe/Zn 0.85 Cd 0.15 Se multi-quantum well (MQW) diode structures with different well thicknesses ( L w ) in the range of 6–13 nm were fabricated, and device characteristics of the diodes were studied in terms of crystalline quality of the MQW layers. In order to investigate the relationship between the device characteristics and the crystalline quality of the MQW layers, the intensity of spontaneous emission from MQW diode structures was measured. The emission intensity increased with increasing L w and showed a maximum value at L w = 10 nm, followed by rather rapid reduction of the emission intensity at L w > 10 nm. This decrease of emission intensity is suggested to be due to the lattice relaxation caused by dislocation formation at the interface taking account of critical thickness of the MQW structure. The lasing characteristics of ZnSe/ZnCdSe MQW blue-green laser diodes are also described.