K. Tappura

Growth of InP, InGaAs, and InGaAsP on InP by gas-source molecular beam epitaxy

Gas-source molecular beam epitaxy (GSMBE), designating the method where the group III beams are derived from the evaporation of solid materials while the group V beams are derived from the high-temperature cracking of AsH3 and PH3, is a very promising method. We show in this work that using indium of high purity and optimizing the growth conditions, unintentional impurities in these films prepared by GSMBE can be reduced to a level comparable to that obtained by all-vapor-source chemical beam epitaxy (CBE). The films grown by GSMBE are of very high quality, as deduced from the measurements of electrical, optical, and structural properties. Furthermore, we have found that the alloy composition in InGaAsP for the wavelength λ of 1.1 μm changes significantly in a range of growth temperature from 525 to 530°C, likely due to an abrupt change in the sticking probability of phosphorus. We have also found that the phosphorus-to-gallium flux ratio strongly affects surface morphology of InGaAsP for λ = 1.3 μm.

Growth of Ga0.29In0.71As0.61P0.39 (λ ≈ 1.3 μm) on InP by gas source molecular beam epitaxy

Abstract The surface morphology of GaInAsP layers for wavelengths near 1.3 μm grown on InP substrates was found to become poor under growth conditions which were only slightly different from the near optimum growth conditions. The substrate temperature was found to be a critical parameter. The quality of the films with negative lattice mismatch differed significantly from those with positive mismatch. In addition, double-crystal XRD features from the layers with poor surface morphology were considerably declined.

Interface effects on electrical properties of high purity InP grown by gas-source molecular beam epitaxy

Abstract The effect of the substrate-epilayer interface of InP on Hall mobilities and carrier concentrations at 300 and 77K is studied. It is shown that photoluminescence (PL) and Hall results are contradictory due to the highly conductive interface of InP, which falsifies the Hall results. After correcting mathematically for the interface effect in the Hall results, PL and Hall data show that our InP layers are of high purity and only slightly compensated. The SIMS profiles reveal an accumulation of carbon and silicon at the interface.

The influence of growth conditions on the composition of GaInAsP grown by gas-source molecular beam epitaxy

Abstract We have studied the effect of growth temperature and growth rate on the composition of GaInAsP grown by gas-source molecular beam epitaxy on InP substrates. The composition of GaInAsP was found to be independent of substrate temperature below a transition temperature, approximately 530°C, at which appeared an abrupt change in the group V composition of GaInAsP for the wavelengths 1.05

Unstable regions in the growth of GaInAsP by gas-source molecular beam epitaxy

Abstract GaInAsP quaternary alloys for the wavelengths near 1.3 and 1.55 μm have been grown on InP(001) substrates by gas-source molecular beam epitaxy. Unstable growth related to (miscibility gap induced) composition modulations was found to occur in these alloy compositions. The dependence of stability of the growth on the growth conditions has been studied. Strain, substrate temperature and growth rate were found to have an important effect on the material quality. The layers grown in unstable regions of the growth parameter space exhibited degraded quality according to X-ray diffraction, photoluminescence, Hall measurements, transmission electron microscopy and inspection of the surface morphology. However, the growth conditions for good-quality material could also be found.

Incorporation of group V elements in gas-source molecular beam epitaxy of GaxIn1-xAsyP1-y with x ≈ 0.15 and y ≈ 0.33

Abstract The incorporation of group V materials in GaInAsP grown on InP substrates by gas-source molecular beam epitaxy was studied. The study concentrated on the alloys with energy gaps corresponding to wavelengths near 1.1 μm. An abrupt change was earlier observed in the alloy composition of GaInAsP (λ≈1.05−1.3μm) as a function of substrate temperature. In this paper, I will present new results concerning the abrupt change. Reflection high-energy diffraction was used to examine the changes in the surface reconstruction of the growing layers in order to illuminate the origin of the abrupt change.

Molecular beam epitaxy grown GaInP top cells and GaAs tunnel diodes for tandem applications

Ga/sub 0.51/In/sub 0.49/P solar cells and GaAs tunnel diodes were grown by gas-source molecular beam epitaxy. The effect of various window layer materials, such as Al/sub 0.51/In/sub 0.49/P, Al/sub 0.8/Ga/sub 0.2/As and ZnSe were studied for n-on-p Ga/sub 0.51/In/sub 0.49/P cells. The best carrier collection was obtained with Al/sub 0.51/In/sub 0.49/P window and with graded doping in emitter and base layers. A total-area AM0 efficiency of 14.0% for 2/spl times/2 cm/sup 2/ area has been measured for this cell. The GaAs tunnel diodes were grown with Be-doping for p-type and Si-doping for n-type material. Specific resistance of 0.09 m/spl Omega/cm/sup 2/ and peak tunneling current of 200 A/cm/sup 2/ were obtained for the best GaAs tunnel diodes. In addition, tunneling effect in a n++Ga/sub 0.51/In/sub 0.49/P/p++GaAs diode was observed.

Comparative study of the substrate‐film interfaces of GaAs grown by two molecular beam epitaxial methods

Carrier concentration profiles in the region of a substrate‐film homojunction for n‐ and p‐type GaAs were studied using a capacitance‐voltage carrier profiling technique. The GaAs films were grown on GaAs substrates by molecular beam epitaxy (MBE) and by gas‐source molecular beam epitaxy (GSMBE). The GaAs homojunctions grown by MBE exhibited a much larger reduction in carrier concentration than those prepared by GSMBE. The highest quality interface, without an observable depletion region, was obtained when an additional hydrogen plasma was used during heat treatment prior to GSMBE growth.

Solid source MBE for phosphide-based devices

Phosphorus-based materials are of great importance for many advanced optoelectronic and electronic devices. The most common techniques used for growing phosphorus containing epitaxial structures are MOCVD, GSMBE and CBE. All these growth methods use highly toxic hydrides as group-V sources. As environmental regulations, safety precautions and cost effectiveness are important issues in compound semiconductor business, there is an urge for a simpler and cheaper growth technique. Molecular beam epitaxy using solid sources for both phosphorus and arsenic (SSMBE) would be the simplest choice. However, the problematic physical properties of phosphorus have hampered the use of SSMBE until recently. The new valved cracker technology has overcome the problems associated with the use of solid phosphorus and SSMBE has matured to the level that state-of-the-art phosphorus-based materials and devices can be produced. In this paper, we review some of our results for SSMBE grown phosphide-based devices. These include strained-layer InGaAsP/InP SCH-MQW and strain-compensated InAsP/InGaP/InP MQW lasers emitting at 1.3 /spl mu/m, strained-layer InGaAs/InGaAsP/GaInP QW lasers for 980 nm and 905 nm, 680 nm strained-layer GaInP/AlGaInP QW lasers, and InGaAs/InP HBTs.

Temperature dependency of the composition of GaInAsP grown by GSMBE

We have grown GaInAsP layers on InP substrates by gas-source molecular beam epitaxy and observed an abrupt change in the alloy composition as a function of growth temperature in the GaInAsP alloys for the wavelengths 1.05<λ⪕1.3 μm. In this study we have concentrated on the alloys in the region of wavelength 1.1 μm. We have studied the influence of growth parameters such as growth rate and AsH3 and PH3 pressures on As concentration and on the magnitude of the abrupt change in more detail.