Eizo Miyauchi

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.

Calculation of electronic structure and photoabsorption spectra of monosilane molecules SiH4, SiF4, and SiCl4

The electronic structure, ionization potentials, and photoabsorption spectra of monosilane molecules SiH4, SiF4, and SiCl4 were calculated using the discrete variational (DV) Xα method. Valence molecular orbitals (MOs) of SiH4 consist (from the lowest) of two occupied bonding MOs between Si and H, a1 and t2. Inner valence MOs of SiF4 and SiCl4 consist of the bonding MOs between Si and halogen, a1 and t2, and outer valence MOs consist of bonding MOs a1 and t2, and the MOs e, t2, and t1 localized on halogen. The lowest unoccupied MOs of SiH4 include two antibonding states t2 and a1, and two localized states, e and t2. The lowest unoccupied MOs of SiF4 and SiCl4 are antibonding states a1 and t2 between Si and halogen. Calculated ionization potentials agree well with measured photoelectron spectra.Calculation of the photoabsorption spectrum for Si 2p core excitation for SiH4, SiF4, and SiCl4 shows that peak positions and intensities agree well with measured photoabsorption spectra in both gas and solid phases...

Chemically enhanced focused ion beam etching of deep grooves and laser-mirror facets in GaAs under Cl2 gas irradiation using a fine nozzle

Chlorine‐enhanced GaAs maskless etching has been performed with a novel focused ion beam etching (FIBE) system. The system is composed of an air‐locked ultrahigh vacuum chamber, a 30‐keV Ga+ FIB column, and a fine nozzle. The nozzle irradiates a high‐density Cl2 flux on a desired, small area of the sample while retaining a sufficiently low surrounding gas pressure for stable Ga+ FIB emission. Condensed Ga residues, appearing on the etched surface with no Cl2 gas, could be suppressed under Cl2 gas irradiation. Highly chemically enhanced sputtering yields (up to 50 GaAs molecules per incident ion) were obtained by selecting the optimum relationship between scanning time and Cl2 gas pressure. At the maximum yield, a deep groove (about 6 μm) with a smooth surface was obtained by line‐scanning FIBE. The etching was applied to laser‐mirror formation of an AlGaAs laser. A vertical mirror facet, fabricated in advance by a reactive ion beam etching, was trimmed about one micron thick by line‐scanning FIBE. Light o...

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...

GaAs Growth Using an MBE System Connected with a 100 kV UHV Maskless Ion Implanter

A new molecular beam epitaxy (MBE) system coupled with a 100 kV maskless ion implanter via an ultrahigh vacuum (UHV) sample transfer module was constructed. This system can grow epitaxial layers with ion beam pattern-implantation without exposing a sample surface to the outer atmosphere. Buried Be implanted layers in MBE grown GaAs were fabricated using this apparatus. Because of the contamination-free UHV growth process, the photoluminescent intensity depth profile of the grown crystal showed no degradation at the interface where the MBE growth was interrupted for the ion implantation process.

Focused Si Ion Implantation in GaAs

A 160-keV, submicron-focused Si ion implantation in MBE-GaAs was made using a 100 kV maskless implanter with a Au–Si–Be alloy ion source. Obtained Raman spectra indicated that compared with the implantation current densities of an unfocused ion beam, the higher current density (about 104 times greater) of the focused beam resulted in less implantation-induced and residual (after annealing up to 500°C) damage. Moreover, 850°C annealing led to a higher electrical activity of focused implanted Si-ions but almost the same optical quality of conventional implantation.

Conduction-band edge discontinuity of InGaAs/GaAsSb heterostructures lattice-matched to InP grown by molecular beam epitaxy

Abstract We report, for the first time, the conduction-band edge discontinuity (ΔE c ) of the InGaAs/GaAsSb staggered lineup heterostructure, lattice-matched to InP, grown by molecular beam epitaxy. From the temperature dependence between 330 and 410 K of current-voltage characteristics of InGaAs/GaAsSb single barrier diodes, we found the ΔE c to be 0.47±0.02 eV. We also determined the energy separation between the conduction-band edge in the InGaAs and the top of the valence-band in the GaAsSb to be 0.25±0.03 eV at room temperature.

Application of focused ion beam technology to maskless ion implantation in a molecular beam epitaxy grown GaAs or AlGaAs epitaxial layer for three‐dimensional pattern doping crystal growth

We report on a new microfabrication process in UHV, implemented with a focused ion beam implanter (FIBI)–molecular beam epitaxy (MBE) crystal growth system with a computer controlled ion beam writing system. By using this combination process technology, GaAs/AlGaAs multilayer pattern doping structures are fabricated by iteration of growing a molecular beam epitaxy (MBE) GaAs or AlGaAs layer followed by implanting focused ion beams, arbitrarily choosing such impurity ions as Be ( p‐type) or Si (n‐type). This process technology is considered as a basis for integrating optical or electrical devices three dimensionally. An application of this technology to a new structure for an AlGaAs/GaAs DH laser is also described.

Growth-Interrupted Interfaces in Multilayer MBE Growth of Gallium Arsenide

Growth-interrupted interfaces in Molecular Beam Epitaxy (MBE) have been characterized by C-V measurements and secondary ion mass spectroscopy. Carriers were depleted around the interfaces depending on interruption conditions such as the background vacuum and the interrupted period. For the depleted samples, carbon was detected at the interfaces. This carbon contaminant deteriorated crystal quality at the interface and caused carrier depletion. Using the MBE system combined with a maskless ion implanter in ultrahigh vacuum (UHV), a selectively Si-implanted GaAs multilayer structure was grown without interface degradation.