Band offset

About: Band offset is a research topic. Over the lifetime, 2446 publications have been published within this topic receiving 53450 citations.

Heterojunction semiconductor device

Abstract: A semiconductor device is described for sensing radiant energy incorporating a pn junction formed by two layers of materials each having a different energy band gap to form a heterojunction diode and wherein the layer having the greatest energy band gap fully covers the boundaries or perimeter of the layer having a lesser energy band gap to reduce surface leakage current. Further, a semiconductor device is described for sensing radiant energy incorporating a pn junction formed by two layers of materials each having a different energy band gap to form a heterojunction diode wherein the layer having the greatest energy band gap has spaced-apart P regions to form the anode of the heterojunction diode whereby the heterojunction diode is buried below the surface of the layer having the greatest energy band gap. The invention reduces the problem of surface and bulk leakage across heterojunction diodes.

The influence of band offsets on the IV characteristics for GaN/SiC heterojunctions

Abstract: GaN/SiC heterojunctions can improve the performance considerably for bipolar transistors based on SiC technology. In order to fabricate such devices with a high current gain, the origin of the low turn-on voltage for the heterojunction has to be investigated, which is believed to decrease the minority carrier injection considerably. In this work heterojunction diodes are compared and characterized. For the investigated diodes, the GaN layers have been grown by molecular beam epitaxy (MBE), metal organic chemical vapor deposition, and hydride vapor phase epitaxy. A diode structure fabricated with MBE is presented here, whereas others are collected from previous publications. The layers were grown either with a low temperature buffer, AlN buffer, or without buffer layer. The extracted band offsets are compared and included in a model for a recombination process assisted by tunneling, which is proposed as explanation for the low turn-on voltage. This model was implemented in a device simulator and compared to the measured structures, with good agreement for the diodes with a GaN layer grown without buffer layer. In addition the band offset has been calculated from Schottky barrier measurements, resulting in a type II band alignment with a conduction band offset in the range 0.6–0.9 eV. This range agrees well with the values extracted from capacitance–voltage measurements.

Photoluminescence and band offsets of AlInAs/InP

Abstract: We report the temperature dependence of Al0.46In0.54As photoluminescence (PL) transition energies and Al0.46In0.54As/InP interface staggered line-up luminescence (SLL) energy. The S shape appearing from 4 to 90 K on the energy versus temperature curves of these PL energies is due to extrinsic recombinations. In particular, the S shape of the SLL energy curve versus temperature is probably due to acceptor impurities localized in AlInAs, at the interface (on-edge impurities). The binding energy of on-edge impurities is lower than its value in the bulk material. This explains why the S shape is less pronounced on the SLL than on the AlInAs PL curve. The band offsets were determined by solving the Schrodinger-Poisson equation system with a self-consistent calculation program. At 4.5 K, the conduction and valence band offsets of the Al0.46In0.54As/InP interface were respectively 0.384 eV and 0.295 eV. This is in agreement with the already reported value of 410 meV for the conduction band offset of the lattice-matched Al0.48In0.52As/InP heterostructure. The temperature dependence of the conduction and valence band offsets is shown to be important: respectively 35 meV and 23 meV between 4.5 and 300 K. The Van Vechten-Malloy model (following a thermodynamic approach) for the temperature dependence of the band offsets is compared with our results. The comparison shows only a qualitative agreement.

Heterojunction band offsets and dipole formation at BaTiO3/SrTiO3 interfaces

Abstract: We used a complement of photoemission and cathodoluminescence techniques to measure formation of the BaTiO3 (BTO) on SrTiO3 (STO) heterojunction band offset grown monolayer by monolayer by molecular beam epitaxy. X-ray photoemission spectroscopy (XPS) provided core level and valence band edge energies to monitor the valence band offset in-situ as the first few crystalline BTO monolayers formed on the STO substrate. Ultraviolet photoemission spectroscopy (UPS) measured Fermi level positions within the band gap, work functions, and ionization potentials of the growing BTO film. Depth-resolved cathodoluminescence spectroscopy measured energies and densities of interface states at the buried heterojunction. Kraut-based XPS heterojunction band offsets provided evidence for STO/BTO heterojunction linearity, i.e., commutativity and transitivity. In contrast, UPS and XPS revealed a large dipole associated either with local charge transfer or strain-induced polarization within the BTO epilayer.

Band offsets at the ZnSe/CuGaSe2(001) heterointerface

Abstract: The formation of the ZnSe/CuGaSe₂ heterointerface was studied by x-ray photoelectron spectroscopy (XPS). ZnSe was sequentially grown on CuGaSe₂(001) epilayers. In situ photoemission spectra of the Ga 3d and Zn 3d core levels as well as XPS valence bands were acquired after each deposition step. The valence-band offset is determined to be ΔEV=0.6±0.1 eV. As a consequence, a nearly symmetric "type-I" band alignment for the ZnSe/CuGaSe₂ heterojunction with a conduction-band offset of ΔEC=0.4±0.1 eV is found. Concerning the band alignment ZnSe can, therefore, be expected to be a suitable buffer material for CuGaSe₂-based thin-film solar cells.