Mutsuo Ogura

Flow rate modulation epitaxy of AlGaAs/GaAs quantum wires on nonplanar substrate

Flow rate modulation epitaxy (FME) is applied to the low‐temperature growth of AlGaAs/GaAs quantum wires (QWRs) on nonplanar substrates. The growth selectivity is found to be enhanced greatly by the use of FME, as compared with the conventional metalorganic chemical vapor deposition due to the enhanced migration of Ga species. An AlGaAs/GaAs QWR with a central thickness of about 9 nm and a lateral width of about 28 nm is grown at 600 °C on a V‐grooved substrate. Good photoluminescence properties are observed from the grown QWR, with the peak energy being in good agreement with the calculated energy level of a parabolic shape lateral confinement potential.

Surface‐emitting laser diode with vertical GaAs/GaAlAs quarter‐wavelength multilayers and lateral buried heterostructure

Threshold current of 2 mA at room temperature cw operation is realized in a vertical distributed feedback surface‐emitting laser diode with lateral buried heterostructure (LBH). In this LBH structure, the vertical distributed feedback active region (AlGaAs/GaAs multilayer) is entirely surrounded with n‐ and p‐type AlGaAs cladding layers for minority‐carrier confinement. The far‐field angle is 7°. The beam shape is nearly circular. However, the lasing spectrum is broad (2–3 nm) compared with the conventional edge‐emitting laser. Major differences between the surface‐emitting laser diode presented here and the conventional edge‐emitting laser diode are discussed.

Electrical and Photo-luminescence Properties of ZnSe Thin Films Grown by Molecular Beam Epitaxy: Substrate Temperature Effect

The substrate temperature effect on electrical and PL properties of undoped MBE ZnSe has been investigated. Resistivity (ρ) of the epilayers shows an abrupt change with the substrate temperature (Ts): ρ~106 ohm-cm for Ts~250°C or \gtrsim400°C, while ρ~1 ohm-cm for 280°C\lesssimTs\lesssim370°C. The substrate temperature dependence of PL spectra of the epilayers reveals that (1) the high resistivity is caused by the increase of the SA centers above 400°C and below 250°C, and (2) the diffusion of As and Ga from the GaAs substrate occurs during the growth process.

High‐quality ZnSe thin films grown by molecular beam epitaxy

High‐quality, nominally undoped, low‐resistivity ZnSe thin films are grown by molecular beam epitaxy (MBE). The MBE ZnSe shows the largest peak intensity ratio of the near‐band‐edge emission to the deep center luminescence even at room temperature compared with other epitaxial techniques, which indicates the smallest concentration of complex defects in the MBE ZnSe. From the temperature dependence of electron mobility for MBE ZnSe, we obtained the mobility value as high as 6.9×103 cm2/Vs. This is the highest value ever obtained in epitaxial ZnSe films and indicates the concentration of isolated charged defects as low as 1×1016 cm−3.

Temperature dependent pohotoluminescence investigation of AlGaAs/GaAs quantum wires grown by flow rate modulation epitaxy

The temperature dependence of photoluminescence (PL) properties of AlGaAs/GaAs quantum wire (QWR) grown on V‐grooved substrates by flow rate modulation epitaxy is investigated. PL from a 7.1 nm thick QWR is easily observed even at room temperature. The full width at half‐maximum (FWHM) of the QWR emission peak increases linearly with increasing temperature at low temperatures and becomes almost independent of temperature at high temperatures, while that of a quantum well layer (QWL) sample increases with increasing temperature up to room temperature. The FWHM of QWR is found to be considerably narrower than that of the QWL sample at high temperatures, which is expected theoretically from the sharp one‐dimensional density of states of QWR but has not been clearly observed experimentally.

HIGH SPATIAL RESOLUTION SPECTROSCOPY OF A SINGLE V-SHAPED QUANTUM WIRE

We report on microscopic photoluminescence of a single V-shaped AlGaAs/GaAs quantum wire. The experiments are performed at low temperature by selectively exciting 1 μm2 of the sample. The main photoluminescence line is split into sharp peaks of width less than 0.5 meV and separated by a few meV. The energy position and the intensity of the peaks are characteristic of the scanned quantum wire. First microphotoluminescence results suggest that localization phenomena are predominant in the quantum wire. They are due to the formation of extended monolayer-step islands, larger than the exciton radius, as in the case of high-quality quantum wells.

Fabrication of highly uniform AlGaAs/GaAs quantum wire superlattices by flow rate modulation epitaxy on V-grooved substrates

Abstract A growth condition (growth temperature) which could maintain an identical growth profile of AlGaAs grown on a V-grooved substrate by metalorganic vapor phase epitaxy independent of the growth thickness is established. This condition is applied to the fabrication of highly uniform AlGaAs GaAs quantum wire superlattices (QWR-SLs) by vertical stacking of multiple QWRs on a V-grooved substrate. An AlGaAs barrier layer thickness of about twice that of the GaAs QWR layer is found to be necessary for the complete recovery of the distorted V-groove bottom curvature. A series of 20 period AlGaAs GaAs QWR-SLs are successfully grown by flow rate modulation epitaxy under the developed condition for a stable AlGaAs growth profile. The excellent size uniformity of the vertically stacked QWRs is confirmed by transmission electron microscopy observation and the narrow full width at half maximum of an AlGaAs (135 A ) GaAs (45) A QWR-SL photoluminescence peak.

Temperature dependence on current-voltage characteristics of nickel/diamond Schottky diodes on high quality boron-doped homoepitaxial diamond film

Ni/diamond Schottky diodes were fabricated on boron-doped homoepitaxial diamond films. Temperature dependence on electrical characteristics of the Schottky diodes was investigated in a temperature range 148 to ∼448 K. The current–voltage characteristics of the diodes show excellent rectification behavior. Temperature dependence on the ideality factor and apparent barrier height was determined, including the effect of series resistance. The evaluated ideality factor was observed to decrease from 1.78 to 1.05, while the apparent barrier height increased from 0.95 to 1.55 eV in this temperature range. The temperature dependence of the forward characteristics can be well explained by thermionic-field-emission theory at low temperature and thermionic emission theory at high temperature, respectively. A possible mechanism of the correlation of the ideality factor and barrier height has been proposed.

Distributed Feed Back Surface Emitting Laser Diode with Multilayered Heterostructure

The first distributed feedback surface emitting laser diode is realized with Al0.3Ga0.7As/GaAs multilayered heterostructure. Transverse junction-stripe (TJS) type lateral carrier injection is employed. The threshold current is 120 mA at 150 K with the active layer thickness of 6 µm. The temperature coefficient of the lasing wavelength is equal to a conventional DFB laser diode.

Trench-type narrow InGaAs quantum wires fabricated on a (311)A InP substrate

InGaAs quantum wires (QWRs) with cross sections as narrow as 10 nm×20 nm have been fabricated on a (311)A InP V-grooved substrate under an As2 source. Trench-type InGaAs QWRs consist of (111)A and (331)B facets with an angle of about 22°. Cathode-luminescence and photoluminescence measurements confirmed the luminescence peak arising from the QWRs.