Akira Takamori

GaAs cleaning with a hydrogen radical beam gun in an ultrahigh‐vacuum system

GaAs surface cleaning prior to molecular‐beam epitaxy (MBE) using a new hydrogen radical beam produced by an electron cyclotron resonance plasma in an ultrahigh‐vacuum system is investigated. Residual oxygen and carbon on the GaAs surface after cleaning are monitored in situ with Auger electron spectroscopy. Oxygen and carbon, which are hard to remove by conventional thermal cleaning, can be removed by hydrogen radical (H*) beam irradiation at a substrate temperature of <400 °C. It is verified that the plasma‐dissociated radicals are much more reactive in the gas phase–solid phase surface chemical interaction than the nondischarged molecules. Ga and As stoichiometry is kept after H* beam cleaning. Good crystallinity is obtained according to reflection high‐energy elecron diffraction. By carrier concentration measurement at the interface between the cleaned surface and the in situ MBE‐regrown layer, it is found that H* beam cleaning reduces the interface state concentration. This cleaning technique makes c...

Cleaning of MBE GaAs Substrates by Hydrogen Radical Beam Irradiation

Hydrogen radical beam cleaning of substrates for GaAs MBE growth has been studied. The cleaning effects of carbon and oxygen contaminated by exposure to air and a lower-grade vacuum were investigated using Auger electron spectroscopy (AES), capacitance-voltage (C-V) carrier profiling, and secondary ion mass spectrometry (SIMS). AES signals of contaminants decreased to the detection limit with hydrogen radical irradiation. Carrier depletion around the growth interface was also reduced with decreasing carbon density.

Maskless ion beam writing of precise doping patterns with Be and Si for molecular beam epitaxially grown multilayer GaAs

We have developed a computer‐controlled ion beam writing system with 14‐bit resolution to operate a 100 kV maskless ion implanter combined with an MBE growth chamber for patterned impurity‐doped GaAs/AlGaAs multilayer growth. Performances of various functions of this new computer‐controlled, crystal growth system have been tested. (1) Ion species (Si++, Si+, Be++, Be+) are rapidly selected with minimum astigmatism. (2) Depth impurity doping geometry can easily be controlled by automatically selecting ion charges or semiautomatically changing accelerating voltage. (3) Ion beam diameter and position are precisely monitored and controlled. (4) Ion beam mark detection can be performed with submicron resolution over double layers. (5) Ion beam writing for maskless implantation can be done in arbitrary shapes over the 400 μm square field with assigned impurity, ion dose, and energy, while monitoring ion current and beam diameter. Using this system, we have demonstrated arbitrary pattern implantation and GaAs gr...

Arsenic Pressure Dependence of Interdiffusion of AlGaAs/GaAs Interface in Quantum Well

Arsenic pressure dependence of interdiffusion of AlGaAs/GaAs hetero-interface at a high temperature has been studied by masuring the wavelength shift of photoluminescence in a multi quantum well. It was found that the interdiffusion at the temperature of 850°C was minimized under arsenic pressure of 100 Torr and it was enhanced both under the lower and higher arsenic pressure. Also the degradation of photoluminescence intensity was observed only under the higher arsenic pressure. These properties are considered to be caused by excess vacancies of gallium and aluminum, and their assosiated defects.

Low-noise 650-nm-band AlGaInP visible laser diodes with a highly doped saturable absorbing layer

Stable self-sustained pulsating and low-noise 650-nm-band AlGaInP visible laser diodes were demonstrated by adopting a novel structure, which has a highly doped saturable absorbing (SA) layer. Short carrier lifetime, which is indispensable for self-pulsation, was realized by applying high doping concentration to the p-type SA layer. 500-/spl mu/m-long devices with 51%/51% coated facets were fabricated, resulting in the threshold current of 75 mA at 20/spl deg/C. The temporal output power was measured at the average output power of 5 mW and the stable self-pulsation was observed up to an ambient temperature of 60/spl deg/C. Therefore, the relative intensity noise (RIN) was kept about -140 dB/Hz in temperature ranging from 20/spl deg/C to 60/spl deg/C. Since the refractive index difference could be kept large and the optical mode could be confined effectively, the astigmatism in this work was below 3 /spl mu/m at 5 mW against dc injection current. The lasers operated over 1350 h under the average output power of 5 mW at 60/spl deg/C.

Growth of heavily Be‐doped AlInP by gas source molecular beam epitaxy

Heavily Be‐doped p‐type AlInP layers have successfully grown on (001)GaAs by gas source molecular beam epitaxy (GSMBE) using phosphine (PH3). Net hole concentration (Nh) as high as about 3.5×1018 cm−3 is achieved for the first time. The surface morphology is found to be smooth up to a Be concentration of 3×1019 cm−3. The resistivity for Nh=3.5×1018 cm−3 is as low as 0.3 Ω cm. The improvement of the electrical activity and surface morphology may be ascribed to subhidrides of phosphorus decomposed from PH3 during GSMBE growth.

Si Depth Profiles in Focused-Ion-Beam-Implanted GaAs

Depth distribution of implanted Si into GaAs using a focused-ion-beam (0.2 µm diameter, 160 keV) was profiled by means of differential Hall effect measurement and secondary ion mass spectroscopy. As compared to conventional unfocused-ion-beam implantation, implantation with a focused ion beam of high current density at high doses results in broadened profiles of the implanted Si at greater depths. This is probably caused by radiation-enhanced migration of the implanted Si during implantation.

Stable operation of self‐sustained pulsation in 650‐nm‐band AlGaInP visible lasers with highly doped saturable absorbing layer

Self‐sustained pulsating 650‐nm‐band AlGaInP visible lasers were fabricated by adopting a new structure, which has a highly doped saturable absorbing (HDSA) layer. Since the doping level and the thickness of the HDSA layer could be controlled accurately by using metalorganic vapor phase epitaxy growth technique, a stable operation of self‐sustained pulsation up to 60 °C was obtained. The lasers operated over 1350 h under the average output power of 5 mW at 60 °C. The relative intensity noise values were below −136 dB/Hz in the temperature ranging from 20–60 °C and remained unchanged after life test.

Study of AlInP and GaInP grown by gas source molecular beam epitaxy (GSMBE)

The electrical, optical and structural properties of Al0.5In0.5P and Ga0.5In0.5P layers grown on (001) GaAs substrates by gas source molecular beam epitaxy (GSMBE) using phosphine (PH3) gas have been studied. For heavy Be doping, the electrical activity was found to be unity up to atomic Be concentration of 2 × 1018 cm-3 in Al0.5In0.5P and 3 × 1019 cm-3 in Ga0.5In0.5P. The maximum hole concentrations achieved are 3.5 × 1018 cm-3 in Al0.5In0.5P and 4 × 1019 cm-3 in Ga0.5In0.5P. 20 K photoluminescence (PL) measurements for heavily Be-doped Al0.5In0.5P showed that the decrease in electrical activity is due to deep levels resulting possibly from Al-Be related defects. An ordered structure and a compositional modulated structure were first observed in Ga0.5In0.5P grown by GSMBE. The degree of ordering was found to be less perfect than that for metalorganic vapor phase epitaxy (MOVPE) due to the lower growth temperature. Typical 300 K PL energy was found to be 1.88 eV which was 20 meV lower than the “normal” energy (1.9 eV).

Formation of submicron isolation in GaAs by implanting a focused boron ion beam emitted from a Pd–Ni–Si–Be–B LM ion source

We have developed a new type of alloyed liquid metal ion source for maskless ion implantation in III–V compound semiconductors. This ion source with alloys consisting of Pd (50), Ni (26), Si (5), Be (6), and B (13) is capable of emitting Si (n‐type dopant), Be (p‐type dopant), and B (device isolation) ions. Using this ion source, active regions (n‐type GaAs, 2×1017/cm3) were isolated by single line implantation with a 100 keV focused B+ ion beam of 0.1 μm diam. A good isolation of submicron width (less than 0.5 μm) has been obtained. The resistivity of these isolated regions implanted with 2×1014 to 2×1015 ions/cm2 is found to be 104 to 105 Ω cm with breakdown voltages of 4 to 10 V after a heat treatment at 800 °C for 20 min. This result indicates that the submicron isolation using this technology can be maintained through the high‐temperature device fabrication process.