Takao Takenaka

Characterization of AiGaP/GaP Heterostructures Grown by MOVPE

Abstract High quality Al x Ga 1- x P/GaP heteroepitaxial layers were grown by a barrel-type multiwafer metalorganic vapor phase epitaxy system. Fundamental aspects concerning the growth and the heterostructures, such as distribution coefficient of Al, critical layer thickness, doping properties, and band discontinuities at the heterojunctions, have been investigated.

Electron traps in dislocation-free In-alloyed liquid encapsulated Czochralski GaAs and their annealing properties

Electron traps in dislocation‐free In‐alloyed liquid encapsulated Czochralski (LEC) GaAs have been studied by deep level transient capacitance spectroscopy. Five traps are observed with activation energies ranging from 0.26 to 0.79 eV below the conduction band. The energies are closely equal to the ones observed in undoped LEC GaAs. However, a notable difference between the In‐alloyed crystal and the undoped crystal exists in effects of annealing on the deep levels. For the In‐alloyed crystal, all levels except EL2(0.79 eV) are unstable under the annealing at 850 °C, while for the undoped crystal, levels EL5(0.41 eV) and EL2 remain stable.

Evaluation of Microdefects in As-Grown Silicon Crystals

Microdefects, revealed as ‘flow patterns’ by preferential etching using Seccos etchant, in as-grown silicon crystals have been investigated by means of a transmission electron microscopy and a preferential etching. In as-grown CZ crystals, grown at the pulling speeds of 0.4 or 1.4 mm/min, dislocation loops and clusters were observed with TEM. The dislocation loops in both crystals are interstitial type. From a thermal behavior of flow patterns by heat treatments, we confirmed that the defects revealed as flow patterns in CZ crystals do not have a similar nature of that in D-defect region of FZ crystals.

Deep levels in semiconducting In-alloyed bulk n-GaAs and its resistivity conversions by thermal treatments

Thermal conversions of resistivities have been studied for In‐alloyed semiconducting (100–106 Ω cm) n‐GaAs grown by the liquid‐encapsulated Czochralski method. These dislocation‐free as‐grown crystals are converted into semi‐insulating (>107 Ω cm) crystals by annealing at 950  °C for 2 h followed by a fast cooling. Such semi‐insulating crystals can be converted further into crystals with lower resistivities (∼106 Ω cm) by treating them at 470  °C for 100 h. In the analysis of the as‐grown samples by the temperature‐dependent Hall measurements, four levels have been found with activation energies 0.13, 0.20, 0.42, and 0.50 eV. It has been shown that these resistivity conversions are induced by concentration changes of the deep states other than the midgap donor EL2, some of them being the levels found in this study.

Photoluminescence Studies on Semi-Insulating In-Doped Dislocation-Free GaAs Grown by LEC Method

Photoluminescence studies were performed at 4.2 K for In-doped dislocation-free GaAs. Large inhomogeneity of carbon-related PL intensity was observed along axial growth direction in an as-grown ingot. It was revealed that the PL intensity was strongly affected by thermal history to which it was subjected during crystal growth. After wafer or ingot annealing, the PL intensity increased and the inhomogeneity was imporved significantly. These observations cannot be explained only by concentrations of carbon and deep donor EL2. Consequently, the PL intensity depends mainly on nonradiative recombination centers and less on EL2.

Nitrogen doping in AlGaP grown by metalorganic vapor phase epitaxy using ammonia

Doping characteristics of nitrogen in AlGaP grown by metalorganic vapor phase epitaxy have been investigated using ammonia as the nitrogen source. It was found that nitrogen could be successfully incorporated into AlGaP up to as much as 1×1020/cm3 assisted by the gas phase parasitic reaction between trimethylaluminum and ammonia, while nitrogen incorporation into GaP was difficult. Nitrogen incorporation was found to be dependent on several factors such as ammonia concentration, Al composition, V/III ratio, and growth temperature. Exciton recombination bound to isoelectronic nitrogen in AlGaP was observed for the first time by photoluminescence measurement.

Observation of microdefects in indium-doped GaAs crystals by preferential etching and infrared light scattering tomography

Abstract Microdefects in indium-doped GaAs crystals grown by the liquid encapsulated Czochralski (LEC) technique were investigated by using preferential Abrahams-Buiocchi etching (AB etching) and infrared light scattering tomography. Elliptical pits were observed on AB etched (100) surfaces in dislocation-free regions at the front of the ingot, not observed at the tail. The elliptical pits are considered to correspond to microprecipitates. Furthermore, an attempt to improve the homogeneity along the growth direction, the effect of heat treatment on the density of the defects, was investigated.

Infrared spectrophotometry of carbon-induced localized vibrational mode in indium-doped liquid-encapsulated czochralski GaAs

Infrared absorption measurements are performed for a carbon‐induced localized vibrational mode in indium‐doped semi‐insulating GaAs crystals. Increase of the indium concentration in GaAs is found to result in a shift of the absorption peak to the lower energy side and a broadening of full width at half‐maximum of the peak. The peak shift of 1 cm−1 corresponds to the change of indium concentration by 2.7×1020 cm−3. For a quantitative analysis of carbon, infrared absorptions are compared with carbon concentrations measured by secondary ion mass spectrometry. The absorption intensity of 1 cm−2 is found to correspond to the carbon concentration of (2.3±1.0)×1016 cm−3.Infrared absorption measurements are performed for a carbon‐induced localized vibrational mode in indium‐doped semi‐insulating GaAs crystals. Increase of the indium concentration in GaAs is found to result in a shift of the absorption peak to the lower energy side and a broadening of full width at half‐maximum of the peak. The peak shift of 1 cm−1 corresponds to the change of indium concentration by 2.7×1020 cm−3. For a quantitative analysis of carbon, infrared absorptions are compared with carbon concentrations measured by secondary ion mass spectrometry. The absorption intensity of 1 cm−2 is found to correspond to the carbon concentration of (2.3±1.0)×1016 cm−3.

Novel evaluation method of silicon epitaxial layer lifetimes by photoluminescence technique

A novel method, the short wavelength laser excited photoluminescence (PL) technique at room temperature, is applied to evaluate carrier lifetime characteristics of silicon epitaxial (epi) layers, which are grown on heavily doped p+ substrates with approximately 1019 cm-3 of boron. The band-edge PL intensity of the epi-layer is closely related to the carrier recombination lfietime at room temperature. The carrier excitation at 488 nm wavelength and the existence of the p/p+ structure, which acts as a stopper for the excess carrier diffusion, enable one to evaluate the epi-layer lifetime characteristics of the epi-layer thicker than 3 micrometers . Applying the method to epi-quality evaluation of the p/p+ epi-wafers, trace metallic contamination in epi-layers introduced by the epi- growth processes has been evaluated successfully. It has been found that a dilute HF cleaning is enough for the sample preparation instead of surface passivation heat treatment, which is usually required for other lifetime measurements. This is a great advantage of the method which enables one to do an in-line epi-quality monitoring. We also found that molybdenum contamination degraded the epi-lifetime and the time dependent dielectric breakdown of thin oxide films grown on p/p+ epi-wafers in this study.

Study of Applicability of AC Photovoltaic Method and Photoconductive Decay Method Using Microwaves as Noncontact Methods for Bulk Lifetime Measurement

The applicability of the ac photovoltaic method and photoconductive decay method using microwaves (µ-PCD method) as bulk lifetime measurement methods were studied. Lifetimes measured by these two methods were compared with bulk lifetimes measured by the photoconductive decay method standardized by ASTM:F28-75. Lifetimes measured by the ac photovoltaic method were in good agreement with the bulk lifetimes of less than 3 ms for both n-type and p-type samples. However, lifetimes measured by the µ-PCD method were significantly lower than the bulk lifetimes. It is concluded that the ac photovoltaic method is a reliable noncontact method for the bulk lifetime measurement of the samples with bulk lifetimes less than 3 ms.