Toshiro Hayakawa

Surface reconstruction limited mechanism of molecular‐beam epitaxial growth of AlGaAs on (111)B face

We propose a model which gives a fundamental limiting factor for the growth of epilayers on (111)B face. Our model is that the As‐trimer structure of As‐stabilized (111)B surface with the (2×2) reconstruction disturbs the incorporation of group III atoms into lattice sites. This model gives the explanation to most of the reported properties in the growth of GaAs and AlGaAs on (111)B substrates. This model has been verified by comparing the growth rate of GaAs layers grown by molecular‐beam epitaxy over mesa‐shaped substrates with (111)A and (111)B sidewalls using As4 and As2. Moreover, the cause of microtwins found in transmission electron microscopy images of AlGaAs grown on (111)B GaAs at a low Ts can be at least partly explained by this model.

Molecular beam epitaxial growth of AlxGa1-xAs (x=0.2-0.7) on (111)B-GaAs using As4 and As2

Basic properties of AlxGa1−xAs (x=0.2–0.7), grown by molecular beam epitaxy on 0.5°‐tilted (111)B‐GaAs, are studied. We have employed the wide substrate temperature, Ts, range of 540–740 °C and different As species; As4 and As2. The surface morphology has been found to depend strongly upon the As species; a specular surface morphology cannot be obtained when using As2 whereas a specular smooth surface can be obtained at high temperatures when using As4. Photoluminescence intensity of n‐Al0.3Ga0.7As (Si=1×1018 cm−3) grown at low Ts (<620–630 °C) does not depend upon the As species and is considered to be determined by defects, such as microtwins and stacking faults, which have been observed by transmission electron microscopy. At high Ts (≳650 °C) photoluminescence intensity is lower for the case of As2 than As4 and this could be due to point defects, such as As interstitials and/or antisite As (AsGa). Deep level transient spectroscopy has been measured on n‐Al0.7Ga0.3As grown on (100)‐ and (111)B‐substrat...

High quality In0.2Ga0.8As/AlxGa1−xAs (x=0−0.32) strained single quantum wells grown by molecular beam epitaxy

The effect of the Al composition on photoluminescence (PL) in the In0.2Ga0.8As/AlxGa1−xAs single strained quantum wells with the well width of 6 nm has been studied. The samples have been grown by molecular beam epitaxy. The PL intensity measured at RT very rapidly increases with the AlAs mole fraction possibly due to the suppression of the carrier leakage from a quantum well. It increases by a factor of 300 when the AlAs mole fraction x is increased from 0 to 0.32. The full width at half maximum of the PL spectrum measured at 10 K is as small as 3.0, 4.4, and 4.9 meV for x=0, 0.14, and 0.32, respectively. The increase in the PL linewidth can be explained by the increased effect of heterobarrier height on the quantized energy. The present results suggest that performance characteristics of devices can be improved by employing the high‐quality AlGaAs barrier instead of GaAs.

Uniform MBE growth of 2 inch diameter wafer for GaAs/AlGaAs and InGaAs/AlGaAs quantum well lasers

Abstract Uniform GaAs/AlGaAs and InGaAs/AlGaAs quantum well lasers have been grown by molecular beam epitaxy at high temperatures, where the desorption of Ga or In cannot be neglected. This is achieved by the uniform temperature distribution in our newly developed In-free holder. The graded-index separate-confinement heterostructure (GRIN-SCH) laser with a GaAs quantum well grown at 720°C has shown the threshold current I th of 72±4 mA and the emission wavelength λ of 854.7±0.8 nm. The GRIN-SCH laser with an InGaAs strained single quantum well has been grown at 570°C for an InGaAs well and at 720°C for AlGaAs cladding and GRIN layers without growth interruption. I th is 53±3 mA and λ is 975.5±5.3 nm. The larger variation of λ results from the nonuniform temperature transient just before the growth in InGaAs.

Limiting mechanism of molecular beam epitaxial growth of AlGaAs on (111) face

Abstract AlGaAs layers have been grown on GaAs(100) and 0.5° -misoriented GaAs(111)B substrates by molecular beam epitaxy using As 4 and As 2 . The quality of (111)B-oriented AlGaAs becomes poorer when more As-stabilized growth conditions are employed; such as higher As pressure, lower substrate temperature and the use of As 2 instead of As 4 . We propose a model where the As-trimer structure of As-stabilized (111)B surface with the (2 × 2) recoonstruction disturbs the incorporation of group III adatoms into lattice sites. In order to confirm this model, we have grown GaAs layers with thin AlAs marking layers over mesa-shaped GaAs(100) substrates with (111)B and (111)A side walls, and observed that the growth rate of GaAs on the (111)B face is very much reduced by using As 2 as compared with the growth using As 4 . This indicates the difficulty of Ga incorporation into the (111)B face, which is not the case for the (111)A face.

Comparison of As species (As4 and As2) in molecular beam epitaxial growth of AlxGa1−xAs (x=0.2–0.7) on (100) GaAs

Systematic studies have been made for the first time on the basic properties of AlxGa1−xAs (x=0.2–0.7) grown by molecular beam epitaxy in the wide growth temperature range of 540–780 °C with As4 and As2. The forbidden growth temperature region (FTR), where the specular smooth surface cannot be obtained, has been found to depend strongly upon both the As species and the AlAs mole fraction x. FTR does not change with x in the case of As4; however, in the case of As2, FTR does not exist for x=0.2 and it increases with x from 0.3–0.7. Photoluminescence of n‐Al0.3Ga0.7As (Si=1×1018 cm−3) grown with As2 shows lower intensity and higher sensitivity to growth temperature than those of samples grown with As4. Deep level transient spectroscopy has been measured on n‐Al0.7Ga0.3As (Si=2×1016 cm−3). New electron traps are found in layers grown with As2.

In0.2Ga0.8As single strained quantum well lasers with GaAs/AlGaAs short‐period superlattice barrier layers grown by molecular beam epitaxy

In0.2Ga0.8As single strained quantum well lasers with GaAs/Al0.45Ga0.55As short‐period superlattice barrier (SPSB)layers have been successfully prepared using molecular beam epitaxy although a part of SPSB has been grown in the forbidden temperature region for AlGaAs, where the specular smooth bulk AlGaAs cannot be grown. The averaged AlAs mole fraction of the present SPSB is 0.25, which gives the heterobarrier height larger than that of the conventional GaAs barrier layers. The threshold temperature sensitivity factor T0 of the laser with SPSB has been measured to be as low as 240 K, which is much larger than that of 90 K in the laser with GaAs barrier layers. This improvement results from the reduction of carrier leakage from quantum well to barrier layers.

High power AlGaAs quantum well laser diodes prepared by molecular beam epitaxy

Stable and reliable AlGaAs high power single quantum well lasers prepared by molecular beam epitaxy have been realized. We have prepared both 50‐μm devices operating in multiple modes and ridge‐waveguide single transverse‐mode devices. Good reliability has been confirmed under the operating condition of 500 mW at 50 °C for the former type of devices and under the condition of 50 mW at 50 °C for the latter type of devices over 1000 h. These results indicate that molecular beam epitaxy is capable of making reliable high power laser diodes.

Effects of growth temperature and substrate misorientation in InGaAs/GaAs strained quantum wells grown by MBE

In GaAs/GaAs single strained quantum wells have been grown by molecular beam epitaxy on (100)-GaAs substrates misoriented by 0°, 4°, and 8° toward (111)A in a wide temperature Ts range of 520–660°C. We have found that the shift of photoluminescence peak wavelength with the misorientation angle is opposite in the cases of low Ts 640°C. The shift to shorter wavelengths at low Ts is attributed to the disordering of the natural superlattice formed in the InGaAs quantum well. The shift to longer wavelengths at high Ts indicates that the incorporation rate of In adatoms increases with the density of steps and kink sites at the growing surface.