A study of the electrical and optical properties of Si delta-doped GaAs layers grown by MBE on a (111)A GaAs surface misoriented toward the [2\bar 1\bar 1] direction

Electrical and photoluminescence studies of MBE-grown Si delta-doped GaAs structures at a varied partial pressure ratio P _As /P _Ga =γ on substrates with (111)Ga orientation and misoriented toward the [2 $\bar 1\bar 1$ ] direction have been performed. Hall effect measurements demonstrated that the conduction type changes from p to n on raising the As pressure (i.e., γ). The observed changes in the photoluminescence spectra are interpreted in terms of a kinetic approach based on different dangling bond densities on terraces and steps of the vicinal surface appearing on [2 $\bar 1\bar 1$ ] substrates misoriented toward the [2 $\bar 1\bar 1$ ] direction.     

Liquid phase epitaxial growth and characterization of InAsxSb1−;x AND In1−yGaySb ON (111)B InSb substrates

Liquid phase epitaxial growth of InAs_xSb_1−x, for 0<_x<0.27 and In_1−yGa_ySb, for 0<y<0.37, has been successfully accomplished on (111)B InSb substrates between the temperatures of 450 and 520°C. The phase diagrams and the growth conditions for high-quality planar epitaxial layers have been determined. For growth of InAs_xSb_1−x for high values of x, the strong tendency of the ternary melt to dissolve the substrate, even when the liquid is a few degrees below its melting point, was negated by using large supercooling. Small supercooling of zero to 5.6°C were required over the whole range of composition examined for (In.Ga)Sb, whereas, for example, supercooling greater than 30°C was required to grow InAs_o.26Sb_o.74 to avoid substrate dissolution. Lattice mismatch to the substrate was relieved by compositional grading. Etch pit studies in both materials yielded dislocation densities ranging from 5.8 × 10² to 2×10⁶ cm⁻² with most materials in the low 10⁴ range. Hall and resistivity measurements performed at 300K and 77K on most samples showed an impurity contamination of the epitaxial layers. Some samples were n-type (carrier concentration approximately 10¹⁷/cm³), with varying degrees of acceptor compensation and others were n-type (carrier concentration approximately l0¹⁷/cm³) at room temperature due to intrinsic conduction, but exhibited p-type conduction (carrier concentration approximately 5×l0^l6/cm³) at 77K. Hall measurements performed on one of the latter samples ofvery low As content from 77K to 4.2K to examine hole freeze-out yielded an acceptor level ionization energy of 0.0126eV which is close to the effective mass acceptor level ionization energy in InSb. The electron-to-hole mobility ratio was also found to be 65.9. Electron microprobe analysis showed silicon to be the dominant impurity.     

Photoluminescence study of type-II GaAs quantum well wires grown on nano-faced (3 1 1)A surface: Quasi-1D exciton observation?

GaAs/AlAs corrugated superlattices (CSLs) grown on nano-faceted (3 1 1)A GaAs surface were studied using Raman spectroscopy and photoluminescence (PL) techniques. Raman data (splitting of localized transversal optical phonons) have proved structural anisotropy of the CSLs. The structural anisotropy leads to optical anisotropy appeared in strong polarization dependence of PL. Temperature dependence of PL has shown that the CSLs are type-II superlattices. Additional peak in PL spectrum at low (77–100 K) temperatures can be result of quasi-1D exciton appearance in the CSLs.     

A comparative study of Cd‐ and Zn‐compound buffer layers on Cu(In1−x,Gax)(Sy,Se1−y)2 thin film solar cells

This paper reports a comparative study of Cu(In,Ga)(S,Se)₂ (CIGSSe) thin‐film solar cells with CBD‐CdS, CBD‐ZnS(O,OH) and ALD‐Zn(O,S) buffer layers. Each buffer layer was deposited on CIGSSe absorber layers which were prepared by sulfurization after selenization (SAS) process by Solar Frontier K. K. Cell efficiencies of CBD‐CdS/CIGSSe, CBD‐ZnS(O,OH)/CIGSSe and ALD‐Zn(O,S)/CIGSSe solar cells exceeded 18%, for a cell area of 0.5 cm². The solar cells underwent a heat‐light soaking (HLS) post‐treatment at 170 °C under one‐sun illumination in the air; among the three condtions, the ALD‐Zn(O,S)/CIGSSe solar cells showed the highest cell efficiency of 19.78% with the highest open‐circuit voltage of 0.718 V. Admittance spectroscopy measurements showed a shift of the N₁ defect's energy position toward shallower energy positions for ALD‐Zn(O,S)/CIGSSe solar cells after HLS post‐treatment, which is in good agreement with their higher open‐circuit voltage and smaller interface recombination than that of CBD‐ZnS(O,OH)/CIGSSe solar cells. Copyright © 2015 John Wiley & Sons, Ltd.