K. Rakennus

Tilting of lattice planes in InP epilayers grown on miscut GaAs substrates: the effect of initial growth conditions

Abstract The relative misorientation (tilt) between the epilayer and substrate (400) lattice planes of InP epilayers grown on (100) GaAs substrates misoriented towards the (100) plane was studied by high resolution X-ray diffraction. The epilayers were grown by gas-source molecular beam epitaxy. For the growth temperature of 490–500°C, the direction of the relative tilt was nearly coincident with the direction of the lattice plane tilting of the substrate, according to previous models. In contrary, when a buffer layer was deposited at a lower temperature of 400–450°C prior to growth, an azimuthal rotation of about 45° was found between the directions of the relative tilt and the substrate lattice plane tilting. In order to explain the results, a temperature-dependent anisotropic nucleation model is proposed. The effect of misfit dislocations is also considered.

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.

Model of growth of single‐domain GaAs layers on double‐domain Si substrates by molecular beam epitaxy

Growth of single‐domain GaAs (100) layers on double‐domain Si (100) substrates by molecular beam epitaxy has been investigated. It has been shown that domain orientation of the top layer of GaAs depends on the surface structure of a buffer layer. The size of atomic step heights on the Si surface and the As‐Si interaction temperature before film growth are not important factors in controlling domain orientation. Suppression of an antiphase disorder is explained in terms of nonstoichiometric antiphase boundary annihilation operative during growth.

Characteristics of indium phosphide solar cells bonded on silicon

Indium phosphide solar cells were bonded on silicon substrates by applying a eutectic bonding method. The InP solar cell structure was first grown homoepitaxially on an InP substrate. Gold layers were deposited on top of the InP cell structure and on the Si substrate. These two samples were then put in contact with each other and the structure was heated to 400-500/spl deg/C so that eutectic alloys formed between Au and the semiconductor materials. When cooling the structure, these two samples stuck together. The InP substrate was then removed by selective etching. After the bonding process the solar cell devices were processed by using the standard photolithographic methods. These cells exhibited low leakage currents, quantum efficiencies almost identical to homoepitaxial InP solar cells and conversion efficiencies of 12.9% under AMO illumination and 16.5% under AM1.5 illumination, which are relatively high in comparison to heteroepitaxial InP solar cells.<<ETX>>

High performance laser diode bars with aluminum-free active regions.

We present operating and lifetest data on 795 and 808 nm bars with aluminum-free active regions. Conductively cooled bars operate reliably at CW power outputs of 40 W, and have high efficiency, low beam divergence, and narrow spectra. Record CW powers of 115 W CW are demonstrated at 795 nm for 30% fill-factor bars mounted on microchannel coolers. We also review QCW performance and lifetime for higher fill-factor bars processed on identical epitaxial material.

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.

Effects of rapid thermal annealing on InP layers grown on GaAs substrates by gas‐source molecular beam epitaxy

InP layers were grown on (100) GaAs substrates by gas‐source molecular beam epitaxy and then were annealed by the rapid thermal annealing (RTA) method. The effects of annealing time and temperature on crystalline structure were studied by double‐crystal x‐ray diffraction. Significant improvement in crystalline quality was observed, due to RTA. The smallest linewidth was 315 s of arc for the 2‐μm‐thick layers upon annealing at 940 °C for 10 s. Using lower temperatures and longer annealing times, the linewidths remained broader but the loss of phosphorus was reduced.

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

Advances in production MBE grown GaInP/GaAs cascade solar cells

GaInP/GaAs cascade solar cells with varying top cell base layer thickness were grown by production solid source molecular beam epitaxy (MBE). The MBE growth was optimized with special control over growth related defects resulting in a beginning of life conversion efficiency of 23.2% for a 2/spl times/2 cm/sup 2/ solar cell. Consistent results were obtained with a balloon calibration. An end of life efficiency of 19.8% and power remaining factor of 0.91 were obtained for these cells after 10/sup 15/ cm/sup -2/ 1 MeV electron irradiation. The good radiation resistance was attributed to the GaInP top cell dominated degradation and graded doping profiles of the top cell.

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.