In situ monitoring and benchmarking in UHV of InP GaAsSb heterointerface reconstructions prepared via MOVPE

Thin InP layers were grown by metalorganic vapor phase epitaxy on the ternary compound GaAs0.5Sb0.5 lattice matched to InP 1 0 0 . The heterojunctions were studied with in situ reflectance anisotropy spectroscopy and benchmarked in ultrahigh vacuum with ultraviolet and X ray photoelectron spectroscopy and low energy electron diffraction with regard to the sharpness of the interface. During growth of GaAs0.5Sb0.5 an Sb rich 1 X 3 like reconstruction was observed and during stabilization with TBAs an As rich c 4 x 4 reconstruction. These two different reconstructions of GaAs0.5Sb0.5 1 0 0 , well known from the binaries GaSb 1 0 0 and GaAs 1 0 0 respectively, were used for preparing InP GaAs0.5Sb0.5 heterojunctions. The RA spectra of thin heteroepitaxial InP layers were compared to a well established RA spectrum of MOVPE prepared homoepitaxial, 2 x 1 like reconstructed P rich InP 1 0 0 , that was used as a reference spectrum of a well defined surface. Growing InP on the c 4 x4 reconstructed GaAsSb 1 0 0 surface resulted in a significantly sharper interface than InP growth on 1 X 3 reconstructed GaAsSb 1 0

Growth of an InGaAs GaAsSb tunnel junction for an InP based low band gap tandem solar cell

The hetero interfaces of an InGaAs GaAsSb tunnel junction, embedded into two InP barrier layers, as used in a tandem solar cell, were studied. With regard to the sharpness of these interfaces, different surface preparations and growth procedures were tested. For that, several surface reconstructions of In0 53Ga0 47As grown by metal organic chemical vapor deposition MOCVD were investigated insitu with re amp; 64258;ectance difference spectroscopy RDS and analyzed in ultrahigh vacuum UHV with low energy electron diffraction LEED and X ray photoemission spectroscopy XPS . Depending on the annealing temperature, three different surface reconstructions of MOCVD prepared InGaAs were found As rich 4 3 , 2 4 and III rich 4 2 c 8 2 . Next, thin GaAs0 51Sb0 49 layers were grown on both As rich and III rich InGaAs surfaces. LEED patterns showed the expected c 4 4 reconstruction of the As terminated GaAsSb surface for both preparations, also of the same quality. A signi amp; 64257;cant difference for the Sb to As ratios of thin GaAsSb layers were measured by XPS, indicating that the unusual growth of GaAsSb on a III rich InGaAs surface results in a sharper InGaAs GaAsSb hetero interface. Moreover, we searched for the best preparation procedure of the InP barrier layer on GaAsSb. RDS and a stable growth of the top cell suggested a favorable growth procedure by ramping the growth temperature from 500 to 600 C during the growth of the InP layer. The challenge here was to prepare GaAsSb at the optimum temperature of 500 C, to switch then to the optimum growth temperature of the subsequent layers of 600 C and to produce a well de amp; 64257;ned and sharp interface

In situ monitored MOVPE growth of undoped and p doped GaSb 1 0 0

In situ monitored MOVPE growth of undoped and p doped GaSb 10

Improved structure and performance of the GaAsSb InP interface in a resonant tunneling diode

GaAsSb InP 1 0 0 hetero interfaces were studied with regard to the performance of metal organic chemical vapor deposition MOCVD grown p type resonant tunneling diodes RTDs . For that, thin InP layers were grown by MOCVD on the ternary compound GaAs0.5Sb0.5, which is lattice matched to InP 1 0 0 . Two different surface reconstructions of 1 0 0 GaAs0.5Sb0.5, similar to a reconstruction of either 1 0 0 GaAs or 1 0 0 GaSb, were used for preparing the InP GaAs0.5Sb0.5 hetero interfaces the As rich, c 4 4 and the Sb rich, 1 3 reconstructions. The preparation of the RTDs was identical except for the Sb versus As rich reconstruction of GaAsSb. The RTDs with As rich prepared GaAsSb InP interfaces showed signi amp; 64257;cantly more symmetric I V characteristics than those with the Sb rich interface preparation, demonstrating a clear advantage for the As rich interface preparation. Surfaces were measured insitu with re amp; 64258;ectance difference spectroscopy RDS and analyzed in ultrahigh vacuum UHV with low energy electron diffraction LEED with regard to the sharpness of the interface. The RD spectra of thin hetero epitaxial InP layers grown on GaAsSb 1 0 0 were compared to the well established RD spectrum of MOCVD prepared homo epitaxial, 2 1 like reconstructed P rich InP 1 0 0 , that was used as reference for a well de amp; 64257;ned surface. Growing InP on the c 4 4 reconstructed GaAsSb 1 0 0 surface resulted in a signi amp; 64257;cantly sharper interface than InP growth on 1 3 reconstructed GaAsSb 1 0 0 , a result that was also borne out by highresolution X ray diffraction spectra. r 2005 Elsevier B.V. All rights reserve

Material studies regarding InP based high efficiency solar cells

Aiming at the improvement of the conversion ef amp; 64257;ciency of a monolithic high ef amp; 64257;ciency multi junction solar cell based on the lattice constant of InP different types of low band gap n p solar cells were prepared on the lattice constant of InP via metal organic chemical vapor deposition MOCVD using only non gaseous, so called alternative precursors like tertiarybutylphosphine TBP . Employing this less toxic precursor compared to phosphine an InP single n p solar cell was prepared as reference yielding the highest internal quantum ef amp; 64257;ciency reported in the literature. New materials were introduced on the lattice constant of InP, in particular GaAsSb Egap 0 75 eV and InAlGaAs Egap 1 03 eV . The new absorber materials were compared to more established materials like InGaAs Egap 0 75 eV and InGaAsP Egap 1 03 eV . It will be shown that the latter cell with 18 Al reached an internal quantum ef amp; 64257;ciency close to that of the InGaAsP cel

New materials for InP based high efficiency solar cells

Unfortunately, no appropriate III V compound has been found yet with a band gap in the range of 1eV and the lattice constant of Ge or GaAs. In contrast, III V semiconductors with band gaps in the range of 1 eV can be grown epitaxially on the lattice constant of InP. The materials science challenge arises here for the higher band gaps. Nevertheless, it appears worthwhile to explore the possibilities of low band gap material based on the InP lattice constant. All III V compounds were grown via MOCVD using only non gaseous, i.e. less toxic, precursors like TBP and TBAs instead of PH3 and AsH3. Employing TBP a InP n p solar cell was prepared as reference cell yielding a similar or even higher internal quantum efficiency IQE than the best InP cell reported in the literature. InAlGaAs was employed as a n p cell for the 1eV band gap range. Its QE was compared with the QE of the more established III V compound InGaAsP. Different InGaAsP n p solar cells with band gaps in the range 0.9eV lt;Egap lt;1.2eV were fabricated and their performance will be discusse