P. W. Yu

Photoluminescence identification of ∼77‐meV deep acceptor in GaAs

A study of the photoluminescence emission band at ∼1.44 eV present in GaAs has been made at temperatures between 2–300 K. Changes in photoluminescence excitation intensity, emission energy, and emission intensity as a function of temperature lead to the identification of a 77±2‐meV deep acceptor. The temperature dependence of the emission‐peak energy follows Eagles’ model for the free electron‐neutral acceptor transition. The origin of the acceptor is discussed on the basis of the presence of a high concentration of arsenic vacancies.

Evidence of intrinsic double acceptor in GaAs

Acceptors present in undoped p‐type conducting GaAs have been studied with photoluminescence, temperature‐dependent Hall measurements, deep level transient spectroscopy, and spark source mass spectrometry. It is shown that p‐type conduction is due to presence of the shallow acceptor CAs and the cation antisite double acceptor GaAs. The first and second ionization energies determined for GaAs are 77 and 230 meV from the valence‐band edge.

Effect of growth interruptions on the light emission and indium clustering of InGaN/GaN multiple quantum wells

InGaN/GaN multiple quantum wells (MQWs) grown with various growth interruptions between the InxGa1−xN well and GaN barrier by metalorganic chemical vapor deposition were investigated using photoluminescence (PL), high-resolution transmission electron microscopy, and energy filtered transmission electron microscopy (EFTEM). The integrated PL intensity of the MQWs with growth interruptions is abruptly reduced compared to that of the MQW without growth interruption. Also, as the interruption time increases the peak emission shows a continuous blueshift. Evidence of indium clustering is directly observed both by using an indium ratio map of the MQWs and from indium composition measurements along an InGaN well using EFTEM. The higher-intensity and lower-energy emission of light from the MQW grown without interruption showing indium clustering is believed to be caused by the recombination of excitons localized in indium clustering regions and the increased indium composition in these recombination centers.

Effect of buffer layers and stacking faults on the reduction of threading dislocation density in GaN overlayers grown by metalorganic chemical vapor deposition

We have studied the effect of the trimethylgallium (TMGa) flow rate in the GaN buffer layer on the optical and structural quality. From low temperature photoluminescence measurements, a GaN overlayer grown on a buffer layer with the TMGa flow rate of 80 μmol/min shows the intense donor-acceptor pair transition peak at 3.27 eV and the weak yellow band emission at 2.2 eV, which are related with stacking faults and threading dislocations from transmission electron microscopy images, respectively. As the TMGa flow rate of the GaN buffer increases, the threading dislocation density rapidly decreased and stacking faults increased in the GaN overlayers. Also, a total threading dislocation density at the optimum condition of the buffer layer is the very low 1×108 cm−2, which is due to the interaction of stacking faults with the vertical threading dislocations and the bending of threading dislocations near the stacking faults. High-resolution x-ray diffraction results show that a high density of stacking faults is...

Determination of interfacial quality of GaAs‐GaAlAs multi‐quantum well structures using photoluminescence spectroscopy

Well size fluctuations have been observed in high quality GaAs‐Ga0.75Al0.25As multi‐quantum well structures having very sharp photoluminescence transitions. The effect of well size fluctuations appears as multiple peaks in both the heavy hole free exciton and the heavy hole donor bound exciton transitions. The observed energy separation of the peaks corresponds to what would be expected for a change in well thickness of 1/2 monolayer. The observed linewidths and the well size fluctuations suggest that these are interlayer rather than intralayer fluctuations. These results are different from earlier reported work. The very narrow emission lines reflect the excellent structural quality of the layers. A model to explain the effective half‐monolayer well size fluctuations is proposed.

Semiconducting/Semi-Insulating Reversibility in Bulk GaAs

Bulk, liquid‐encapsulated Czochralski GaAs may be reversibly changed from semiconducting (ρ∼1 Ω cm) to semi‐insulating (ρ∼107 Ω cm) by slow or fast cooling, respectively, following a 5 h, 950 °C soak in an evacuated quartz ampoule. This effect has been studied by temperature‐dependent Hall‐effect, photoluminescence, infrared absorption, mass spectroscopy, and deep level transient spectroscopy measurements. Except for boron, the samples are very pure, with carbon and silicon concentrations less than 3×1014 cm−3. Donor and acceptor concentrations, on the other hand, are in the mid 1015 cm−3 range, which means that the compensation is primarily determined by native defects, not impurities. A tentative model includes a donor at EC−0.13 eV, attributed to VAs−AsGa, and an acceptor at EV+0.07 eV, attributed to VGa−GaAs.

Deep-center photoluminescence in undoped semi-insulating GaAs: 0.68 eV band due to the main deep donor

Abstract The 0.68 eV photoluminescence band present in undoped semi-insulating GaAs crystals has been studied with the change of temperature. It is shown that the 0.68 eV band is due to the radiative transition involving a main deep donor and the valence band. The origin of the donor is of an intrinsic origin and may involve an As antisite defect. It is found that the donor level does not change in energy with respect ot the valence band at T = 4–300 K. The donor level is found to be at 0.73 eV from the conduction band at T = 4 K.

Mass‐spectrometric determination of antimony incorporation during III–V molecular beam epitaxy

The antimony incorporation rate α(Sb) during molecular beam epitaxy (MBE) of GaAs1−ySby, AlAs1−ySby, and Al0.5Ga0.5As1−ySby is determined as a function of growth conditions via mass‐spectrometric measurements of the nonincorporated fraction of the incident antimony flux. The observed trends of an increase in Sb incorporation rate with decreasing substrate temperature and increasing group III flux, and an increase in resulting Sb content with Sb flux, are found to be in agreement with previous studies using ex situ techniques only. Additionally, the process of GaAsSb on GaAs interface formation is shown to result in a time dependent α(Sb) and is understood on the basis of a surface Sb‐content dependent Sb desorption rate. Similarly, the Sb desorption rate is found to be time dependent when an incoming Sb flux reacts with a growth interrupted GaAs surface to form a GaAsSb surface layer which is likely to be graded in composition.

Deep photoluminescence band related to oxygen in gallium arsenide

Temperature‐dependent photoluminescence and photoluminescence excitation spectroscopy have been used to measure the 0.63‐eV luminescence band present in O‐doped semi‐insulating GaAs. It is shown that the 0.63‐eV band is related to the presence of O. The center responsible for the band forms a deep level similar to the main deep donor EL2. However, spark source mass spectrometry indicates that incorporation of O into GaAs is difficult.

Persistent photoluminescence quenching of 0.68‐eV emission in undoped semi‐insulating GaAs

The persistent photoluminescence quenching effect is shown to occur on the broad 0.68‐eV emission commonly present in undoped semi‐insulating GaAs bulk materials. The dependence of this persistent emission on below band‐gap energy excitation has been measured. The data indicate involvement of the main deep donor EL2 in the radiative mechanism of the 0.68‐eV emission. The persistent photoluminescence quenching effect can be explained by the presence of both normal and metastable states of EL2.