Epitaxial growth of CuGaSe2 thin films by MBE Influence of the Cu Ga ratio

By molecular beam epitaxy MBE CuGaSe2 CGS thin films with varying Cu Ga ratios were grown epitaxial on GaAs 100 and stepped GaAs 111 A substrates. Cu Ga ratios from Cu poor to Cu rich were obtained. In this work the appearance of Cu crystallites on the surface of epitaxial CGS 001 layers are observed and strategies to avoid these precipitations are presented. High quality thin CGS films of around 100 nm thickness are obtained, enabling a detailed analysis of the electronic and chemical properties as well as of the crystal structure of the CGS surfaces. The electronic structure with respect to the Cu Ga ratio was characterized in situ by XPS and UPS. By LEED a 4x1 Cu poor and near stoichiometric and a 4x2 Cu rich reconstruction of a zinc blende structure were obtained. For CuGaSe2 112 the LEED pattern showed a 3x1 chalcopyrite reconstruction for Cu Ga ratios lt; 1. A 1x1 reconstruction of the chalcopyrite structure was observed for Cu rich 112 samples. The observed dependence of the surface reconstruction on the stoichiometry for CGS grown on GaAs has not been reported in literature so far. Additionally, for Cu rich stoichiometries a binary phase of Cu2 xSe appeared independently of orientation. The film morphology was investigated ex situ by SE

Direct determination of the band offset in atomic layer deposited ZnO hydrogenated amorphous silicon heterojunctions from X ray photoelectroscopy valence band spectra

The chemical composition and band alignment at the heterointerface between ALD grown zinc oxide ZnO and hydrogenated amorphous silicon a Si H is investigated using monochromatized X ray photoelectron spectroscopy. A new approach for obtaining the valence band offset DeltaEV is developed, which consists in fitting the valence band VB spectrum obtained for a Si H with a thin ZnO overlayer as the sum of experimentally obtained VB spectra of a bulk a Si H film and a thick ZnO film. This approach allows obtaining DeltaEV 2.71 0.15 eV with a minimum of assumptions, and also yields information on the change in band bending of both substrate and ZnO film. The band offset results are compared to values obtained using the usual approach of comparing valence band edge to core level energy differences, DeltaEB,CL DeltaEB,VB. Furthermore, a theoretical value for the VB offset is calculated from the concept of charge neutrality level line up, using literature data for the CNLs and the experimentally determined ZnO a Si H interface dipole. The thus obtained value of DeltaEVCNL 2.65 0.3 eV agrees well with the experimental DeltaE

Photoelectron spectromicroscopy at chalcopyrite films

CuInSe2 films were prepared by MBE on GaAs 111 A substrates. ZnSe and ZnO are subsequently deposited in situ by MOMBE. Interface parameters like band offsets and morphology are studied by X ray photoelectron spectroscopy XPS and Low energy electron diffraction LEED . Spectroscopic XPEEM X ray Photo electron emission microscopy at the U49 2 PGM2 beamline at BESSY was used to investigate the lateral homogenity of the interface. After annealing in situ a lateral inhomogenious In diffusion is observed into the ZnSe ZnO interfac

Composition at the CuInSe2 ZnO interface copper depletion induced by diethyl zinc

Abstract The interface formation between epitaxial CuInSe2 112 films and ZnO deposited by metal organic MBE is investigated by photoelectron spectroscopy. Reaction of diethyl zinc with CuInSe2 leads to the formation of an intrinsic ZnSe layer and copper depletion of the interface. This is associated with Zn doping of the chalcopyrite surface and a Fermi level shift towards the conduction band. The implications on the band alignment are discussed

Recent Cases

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Thin film growth and band lineup of In2O3 on the layered semiconductor InSe

Thin films of the transparent conducting oxide In2O3 have been prepared in ultrahigh vacuum by reactive evaporation of indium. X-ray diffraction, optical, and electrical measurements were used to characterize properties of films deposited on transparent insulating mica substrates under variation of the oxygen pressure. Photoelectron spectroscopy was used to investigate in situ the interface formation between In2O3 and the layered semiconductor InSe. For thick In2O3 films a work function of φ = 4.3 eV and a surface Fermi level position of EF−EV = 3.0 eV is determined, giving an ionization potential IP = 7.3 eV and an electron affinity χ = 3.7 eV. The interface exhibits a type I band alignment with ΔEV = 2.05 eV, ΔEC = 0.29 eV, and an interface dipole of δ = −0.55 [email protected]

Laterally inhomogeneous surface-potential distribution and photovoltage at clustered In/WSe₂(0001) interfaces

Small increments of indium were evaporated at 300 and 100 K onto the van der Waals (0001) surface of p-type WSe₂ crystals. The interface formation was investigated in vacuo with x-ray photoemission spectroscopy, ultraviolet photoemisson spectroscopy, soft-x-ray photoemission spectroscopy, and low-energy electron diffraction. Additional scanning tunneling microscopy (STM), scanning electron microscopy (SEM), and microprobe measurements were performed ex situ. For deposition at 300 K a nonreactive interface is formed and the indium layer grows in the Volmer-Weber growth mode. The size and distribution of the In clusters for specific coverages were determined ex situ by STM and SEM. The band bending of 0.55 eV, as determined from binding-energy shifts of the substrate emissions, is far below the expected Schottky-limit value of 1.1 eV. The observed surface-photovoltage (SPV) shifts of the substrate emission lines are smaller (up to 0.2 eV) than those from the adsorbate lines. The maximum adsorbate SPV shift of 0.6 eV at 150 K exceeds the measured band bending, indicating that the band bending beneath the In clusters must be larger than between them. At a sample temperature of 100 K, In forms atomically flat layers (Frank–van der Merwe growth) allowing the determination of the actual band bending of 0.9–1.0 eV below the In-covered surface. For these conditions, the SPV is only 0.1 eV due to an electrical leakage current. During warmup to 300 K, a transition to the clustered interface occurs. For this interface, the band bending below the indium clusters could also be determined from temperature-dependent SPV measurements. The determined barrier height of 1.04 eV is in good agreement with the value measured at the unclustered interface

Electronic band structure of single-crystal and single-layer WS₂: Influence of interlayer van der Waals interactions

The valence band structure of the layered transition metal dichalcogenide WS₂ has been determined experimentally by angle resolved photoelectron spectroscopy and theoretically by augmented spherical wave band structure calculations as based on density functional theory. Good agreement between experimental and calculated band structure is observed for single crystal WS₂. An experimental band structure of a single layer was determined from an electronically decoupled film prepared on a single crystalline graphite substrate by metal-organic van der Waals epitaxy. The polarization dependent photoemission selection rules of the single layer film are appropriate for a free standing film. The experimental single layer band structure shows some differences compared to band structure calculations using bulk atomic positions within the layer. We conclude that relaxation of the single layer occurs as a consequence of the missing interlayer interactions leading to close agreement between electronic structure of the single layer and single crystal. As a consequence of the missing interlayer interactions the valence band maximum for the single layer is located at the K point of the Brillouin zone

Electronically Decoupled Films of InSe Prepared by van der Waals Epitaxy: Localized and Delocalized Valence States

Submonolayer to several monolayer thick films of the layered semiconductor InSe were deposited on highly oriented pyrolytic graphite by van der Waals epitaxy and probed by energy dependent angle resolved photoelectron spectroscopy. The layers show a transition from two-dimensional bands with atomiclike states to molecularlike states localized along the c direction normal to the surface. The extended band structure showing band dispersion was observed for thicker films