Time-resolved photoluminescence measurements reveal a minority carrier lifetime of >412 ns at 77 K under low excitation for a long-wavelength infrared InAs/InAs0.72Sb0.28 type-II superlattice (T2SL). This lifetime represents an order-of-magnitude increase in the minority carrier lifetime over previously reported lifetimes in long-wavelength infrared InAs/Ga1−xInxSb T2SLs. The considerably longer lifetime is attributed to a reduction of non-radiative recombination centers with the removal of Ga from the superlattice structure. This lifetime improvement may enable background limited T2SL long-wavelength infrared photodetectors at higher operating temperatures.

The effects of luminescence coupling on the external quantum efficiency (EQE) measurement of an InGaP/InGaAs/Ge triple junction solar cell were investigated. A small signal model was used to study the interaction of the subcells during EQE measurement. It was found that an optical–electrical feedback mechanism results in EQE measurement artifacts. Measurements of luminescence from the InGaP p–n junction are also performed to quantitatively determine the strength of the luminescence coupling. These results offer a more thorough and comprehensive interpretation of EQE measurement results that are needed for the design and accurate performance evaluation of high‐efficiency multijunction solar cells. The effects demonstrated here can also be used to measure the spontaneous emission efficiency of the subcells, which is useful for nondestructive assessment of multijunction solar cell material quality. Copyright © 2011 John Wiley & Sons, Ltd.

"Measurement of InAsSb bandgap energy and InAs/InAsSb band edge positions using spectroscopic ellipsometry and photoluminescence spectroscopy" (2015). The structural and optical properties of lattice-matched InAs 0.911 Sb 0.089 bulk layers and strainbalanced InAs/InAs 1Àx Sb x (x $ 0.1-0.4) superlattices grown on (100)-oriented GaSb substrates by molecular beam epitaxy are examined using X-ray diffraction, spectroscopic ellipsometry, and temperature dependent photoluminescence spectroscopy. The photoluminescence and ellipsometry measurements determine the ground state bandgap energy and the X-ray diffraction measurements determine the layer thickness and mole fraction of the structures studied. Detailed modeling of the X-ray diffraction data is employed to quantify unintentional incorporation of approximately 1% Sb into the InAs layers of the superlattices. A Kronig-Penney model of the superlattice miniband structure is used to analyze the valence band offset between InAs and InAsSb, and hence the InAsSb band edge positions at each mole fraction. The resulting composition dependence of the bandgap energy and band edge positions of InAsSb are described using the bandgap bowing model; the respective low and room temperature bowing parameters for bulk InAsSb are 938 and 750 meV for the bandgap, 558 and 383 meV for the conduction band, and À380 and À367 meV for the valence band. V C 2015 AIP Publishing LLC.[http://dx

InAs/InAs1−xSbx type II superlattices designed for mid-wavelength infrared photo-detection have been studied using several electron microscopy methods, with specific attention directed towards interface chemical diffusion caused by Sb segregation. Reciprocal-space image analysis using the geometric phase method showed asymmetric interfacial strain profiles at the InAs-on-InAsSb interface. Measurement of local Sb compositional profiles across the superlattices using electron energy-loss spectroscopy and 002 dark-field imaging confirmed asymmetric Sb distribution, with the InAs-on-InAsSb interface being chemically graded. In contrast, the InAsSb-on-InAs interface showed a small intrinsic interface width. Careful evaluation of the experimental Sb composition profiles using a combined segregation and sigmoidal model reached quantitative agreement. Segregation dominated over the sigmoidal growth at the InAs-on-InAsSb interface, and the segregation probability of 0.81 ± 0.01 obtained from the two microscopy techniques agreed well within experimental error. Thus, 81% of Sb atoms from the topmost layers segregated into the next layer during growth causing the interfaces to be broadened over a length of ∼3 nm. This strong Sb segregation occurred throughout the whole superlattice stack, and would likely induce undesirable effects on band-gap engineering, such as blue-shift or broadening of the optical response, as well as weakened absorption.

No abstract