Band offset

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

Band offsets at the CdS/CuInSe2 heterojunction

Abstract: The traditional explanation for the successful electron‐hole separation in CdS/CuInSe2 solar cells rests on the assumption of a type‐II band lineup: The conduction‐band minimum is assumed to be on the CdS window while the valence‐band maximum is assumed to be localized on the CuInSe2 absorber. This picture of negative conduction‐band offset ΔEc<0 was supported by the electron affinity rule, but was sharply contradicted by the more recent photoemission experiments of Nelson et al. for CdS/CuInSe2 yielding ΔEc=+1.08 eV. Our first principles calculations yield for CdS/CuInSe2 ΔEc=+0.31 eV, hence, a type‐I band alignment. We challenge the published experimental value as being in error and point to the need of revising current solar cell device models that assume ΔEc<0.

Recent Progress on 1.55- $\mu{\hbox {m}}$ Dilute-Nitride Lasers

Abstract: We review the recent developments in GaAs-based 1.55-mum lasers grown by molecular beam epitaxy (MBE). While materials growth is challenging, the growth window appears to be relatively broad and is described in detail. The key considerations for producing high-quality GalnNAsSb material emitting at 1.55-mum regime are examined, including the nitrogen plasma conditions, ion removal from the nitrogen flux, surfactant- mediated growth, the roles of various V-II ratios, the growth temperature, the active region thermal budget, proper annealing, and composition. We find that emission may be tuned throughout the 1.55-mum communications band without penalty to the optical quality varying only one parameter - the total growth rate. This powerful result is validated by the demonstration of low-threshold edge-emitting lasers throughout the 1.55-mum regime, including threshold current densities as low as 318 A/cm2 at 1.54 mum. Additional characterization by Z-parameter techniques, cavity length studies, and band offset measurements were performed to better understand the temperature stability of device performance. Lasing was extended as far as 1.63 mum under nonoptimized growth conditions. The GaAs-based dilute-nitrides are emerging as a very promising alternative to InP-based materials at 1.55-mum due to their high gain, greater range of achievable band offsets, as well as the availability of lattice-matched AlAs-GaAs materials and native oxide layers for vertical-cavity surface-emitting lasers (VCSELs). Indeed, this effort has enabled the first electrically injected C-band VCSEL on GaAs.

Valence band structure and band alignment at the ZrO2/Si interface

Abstract: X-ray photoelectron spectroscopy combined with first-principles simulations are used to determine the band alignments of ZrO2 thin films on silicon. Theoretical band offsets were calculated by simulating the ZrO2/Si interface by means of plane-wave pseudopotential calculations. Experimental band offsets were determined by measuring the core-level to valence-band maximum binding energy differences. Excellent agreement was obtained between the theoretical (3.5–3.9 eV) and experimental (3.65 eV) valence band offsets. Both theoretical and experimental analyses predict the conduction band offset to be ∼0.6–1.0 eV which indicates the intrinsic limitation of ZrO2 to be considered as a viable alternative gate dielectric.

Double-heterojunction nanorods

Abstract: As semiconductor heterostructures play critical roles in today's electronics and optoelectronics, the introduction of active heterojunctions can impart new and improved capabilities that will enable the use of solution-processable colloidal quantum dots in future devices. Such heterojunctions incorporated into colloidal nanorods may be especially promising, since the inherent shape anisotropy can provide additional benefits of directionality and accessibility in band structure engineering and assembly. Here we develop double-heterojunction nanorods where two distinct semiconductor materials with type II staggered band offset are both in contact with one smaller band gap material. The double heterojunction can provide independent control over the electron and hole injection/extraction processes while maintaining high photoluminescence yields. Light-emitting diodes utilizing double-heterojunction nanorods as the electroluminescent layer are demonstrated with low threshold voltage, narrow bandwidth and high efficiencies.

CuSbSe2 photovoltaic devices with 3% efficiency

Abstract: Recent technical and commercial successes of existing thin-film solar cell technologies encourage the exploration of next-generation photovoltaic (PV) absorber materials. Of particular scientific interest are compounds that do not exhibit conventional tetrahedral semiconductor bonding, such as CuSbSe2. CuSbSe2 has a 1.1 eV optical absorption onset, a 105 cm−1 absorption coefficient, and a hole concentration of 1017 cm−3. Here, we demonstrate CuSbSe2 PV prototypes with efficiencies >3%, prepared by a self-regulated sputtering process using a conventional substrate device architecture. Bulk recombination, device engineering issues, and a nonideal CuSbSe2/CdS band offset likely limit the promising initial result.