Due to the unique set of properties possessed by ZnO, thin films of ZnO have received more and more interest in the last 20?years as a potential material for applications such as thin-film transistors, light-emitting diodes and gas sensors. At the same time, the increasingly stringent requirements of the microelectronics industry, among other factors, have led to a dramatic increase in the use of atomic layer deposition (ALD) technique in various thin-film applications. During this time, the research on ALD-grown ZnO thin films has developed from relatively simple deposition studies to the fabrication of increasingly intricate nanostructures and an understanding of the factors affecting the fundamental properties of the films. In this review, we give an overview of the current state of ZnO ALD research including the applications that are being considered for ZnO thin films.

https://iopscience.iop.org/article/10.1088/0268-1242/29/4/043001/pdf

Atomic layer deposition of ZnO: a review

p-Type ZnO materials: Theory, growth, properties and devices

Abstract In the past 10 years, ZnO as a semiconductor has attracted considerable attention due to its unique properties, such as high electron mobility, wide and direct band gap and large exciton binding energy. ZnO has been considered a promising material for optoelectronic device applications, and the fabrications of high quality p-type ZnO and p–n junction are the key steps to realize these applications. However, the reliable p-type doping of the material remains a major challenge because of the self-compensation from native donor defects (V O and Zn i ) and/or hydrogen incorporation. Considerable efforts have been made to obtain p-type ZnO by doping different elements with various techniques. Remarkable progresses have been achieved, both theoretically and experimentally. In this paper, we discuss p-type ZnO materials: theory, growth, properties and devices, comprehensively. We first discuss the native defects in ZnO. Among the native defects in ZnO, V Zn and O i act as acceptors. We then present the theory of p-type doping in ZnO, and summarize the growth techniques for p-type ZnO and the properties of p-type ZnO materials. Theoretically, the principles of selection of p-type dopant, codoping method and X Zn –2V Zn acceptor model are introduced. Experimentally, besides the intrinsic p-type ZnO grown at O-rich ambient, p-type ZnO (MgZnO) materials have been prepared by various techniques using Group-I, IV and V elements. We pay a special attention to the band gap of p-type ZnO by band-gap engineering and room temperature ferromagnetism observed in p-type ZnO. Finally, we summarize the devices based on p-type ZnO materials.

RaoP-Type ZnO Materials: Theory, Growth, Properties, and Devices

Series Preface. Preface. Acknowledgements. 1 Structural Properties. 1.1 Ionicity. 1.2 Elemental Isotopic Abundance and Molecular Weight. 1.3 Crystal Structure and Space Group. 1.4 Lattice Constant and Its Related Parameters. 1.5 Structural Phase Transition. 1.6 Cleavage Plane. 2 Thermal Properties. 2.1 Melting Point and Its Related Parameters. 2.2 Specific Heat. 2.3 Debye Temperature. 2.4 Thermal Expansion Coefficient. 2.5 Thermal Conductivity and Diffusivity. 3 Elastic Properties. 3.1 Elastic Constant. 3.2 Third-Order Elastic Constant. 3.3 Young's Modulus, Poisson's Ratio and Similar. 3.4 Microhardness. 3.5 Sound Velocity. 4 Lattice Dynamic Properties. 4.1 Phonon Dispersion Relation. 4.2 Phonon Frequency. 4.3 Mode Gruneisen Parameter. 4.4 Phonon Deformation Potential. 5 Collective Effects and Some Response Characteristics. 5.1 Piezoelectric and Electromechanical Constants. 5.2 Frohlich Coupling Constant. 6 Energy-Band Structure: Energy-Band Gaps. 6.1 Basic Properties. 6.2 E0-Gap Region. 6.3 Higher-Lying Direct Gap. 6.4 Lowest Indirect Gap. 6.5 Conduction-Valley Energy Separation. 6.6 Direct-Indirect-Gap Transition Pressure. 7 Energy-Band Structure: Effective Masses. 7.1 Electron Effective Mass: G Valley. 7.2 Electron Effective Mass: Satellite Valley. 7.3 Hole Effective Mass. 8 Deformation Potentials. 8.1 Intravalley Deformation Potential: G Point. 8.2 Intravalley Deformation Potential: High-Symmetry Points. 8.3 Intervalley Deformation Potential. 9 Electron Affinity and Schottky Barrier Height. 9.1 Electron Affinity. 9.2 Schottky Barrier Height. 10 Optical Properties. 10.1 Summary of Optical Dispersion Relations. 10.2 The Reststrahlen Region. 10.3 At or Near The Fundamental Absorption Edge. 10.4 The Interband Transition Region. 10.5 Free-Carrier Absorption and Related Phenomena. 11 Elastooptic, Electrooptic and Nonlinear Optical Properties 11.1 Elastooptic Effect. 11.2 Linear Electrooptic Constant. 11.3 Quadratic Electrooptic Constant. 11.4 Franz-Keldysh Effect. 11.5 Nonlinear Optical Constant. 12 Carrier Transport Properties. 12.1 Low-Field Mobility: Electrons. 12.2 Low-Field Mobility: Holes. 12.3 High-Field Transport: Electrons. 12.4 High-Field Transport: Holes. 12.5 Minority-Carrier Transport: Electrons in p-Type Materials. 12.6 Minority-Carrier Transport: Holes in n-Type Materials. 12.7 Impact Ionization Coefficient. Index.

Properties of group-IV, III-V and II-VI semiconductors

Journal of Vacuum Science and Technology B: Microelectronics and Nanometer Structures: Preface

This paper reports the proposal, design, and demonstration of ultra-thin GaAs single-junction solar cells integrated with a reflective back scattering layer to optimize light management and minimize non-radiative recombination. According to our recently developed semi-analytical model, this design offers one of the highest potential achievable efficiencies for GaAs solar cells possessing typical non-radiative recombination rates found among commercially available III-V arsenide and phosphide materials. The structure of the demonstrated solar cells consists of an In0.49Ga0.51P/GaAs/In0.49Ga0.51P double-heterostructure PN junction with an ultra-thin 300 nm thick GaAs absorber, combined with a 5 μm thick Al0.52In0.48P layer with a textured as-grown surface coated with Au used as a reflective back scattering layer. The final devices were fabricated using a substrate-removal and flip-chip bonding process. Solar cells with a top metal contact coverage of 9.7%, and a MgF2/ZnS anti-reflective coating demonstrated...

Ultra-thin GaAs single-junction solar cells integrated with a reflective back scattering layer

Stable p-type ZnO films grown by atomic layer deposition on GaAs substrates and treated by post-deposition rapid thermal annealing

CdTe/Mg0.46Cd0.54Te double heterostructures with n-type In doping concentrations, varied from 1 × 1016 to 7 × 1018 cm−3, have been grown on InSb substrates using molecular beam epitaxy. Secondary ion mass spectroscopy measurements show strong diffusion of In from the InSb substrate to the CdTe buffer layer, while the In concentration is constant in the CdTe layer between the two Mg 0.46Cd0.54Te barrier layers. Capacitance–voltage measurements show that the dopants are 100% ionized for the doping concentration range from 1 × 1016 to 1 × 1018 cm −3. The carrier lifetime decreases with increasing doping concentration (from 0.73 μs for an unintentionally doped sample to 0.74 ns for a 1 × 1018 cm−3 doped sample) due to the decrease of both radiative and nonradiative lifetimes. Decent carrier lifetimes are achieved (∼100 ns) between 1 × 1016 and 1 × 1017 cm−3 doping levels, which is beneficial for developing n-type monocrystalline CdTe solar cells, photodetectors, and other optoelectronic devices. The strongest photoluminescence intensity is observed when the doping concentration is 1 × 1017 cm −3, which corresponds to the highest internal quantum efficiency.

Electrical and Optical Properties of n-Type Indium-Doped CdTe/Mg 0.46 Cd 0.54 Te Double Heterostructures

This paper proposes and demonstrates the use of a textured and lattice-matched semiconductor layer coated with a Au reflector for reflective back scattering to enhance the efficiency of single-junction solar cells with ultra-thin absorbers. The device structure studied in this work consists of an In0.49Ga0.51P/GaAs/In0.49Ga0.51P double-heterostructure single-junction solar cell with a GaAs absorber of either 300 nm or 1000 nm thick, as well as a textured Al0.52In0.48P layer coated with a highly reflective Au film. The devices, areas ranging from 0.3×0.3 mm2 to 1×1 mm2, are flip-chip bonded onto Si carrier substrates, covered by a contact metal grid (with a 9.7% or 10.7% shadow area for the 300 nm and 1000 nm devices, respectively) and a MgF2/ZnS anti-reflective coating. Both types of device designs demonstrate an open-circuit voltage of 1.00 V, short-circuit current densities of 24.5 and 26.1 mA/cm2, and power conversion efficiencies of 19.1% and 20.6%, respectively; these measurements are carried out under 1 sun solar radiation (AM 1.5G, 0.1 W/cm2). It is reasonable to expect that the short-circuit current densities and conversion efficiencies of these devices could reach 26.6 mA/cm2 and 28.6 mA/cm2, and 20.7% and 22.6%, respectively, when a typical contact grid layout with 2% surface coverage is used. These short-circuit current densities are only 3.6 and 1.6 mA/cm2 lower than the maximum theoretical value 30.2 mA/cm2, respectively.

Ultra-thin GaAs single-junction solar cells integrated with an AlInP layer for reflective back scattering

This paper studies non-Lambertian scattering and its impacts on the optical properties and device performance of the ultrathin GaAs single-junction solar cell with a reflective back scattering layer. The Phong distribution is used to quantify the scattering effectiveness of the textured back surface, as well as its impacts on device absorptance, emittance, photon extraction and recycling factor, short-circuit current density $(J_{{\rm sc}})$ , external quantum efficiency (EQE), and power conversion efficiency. Both a general GaAs cell design and the ultrathin cell design are carefully investigated. A Phong exponent m of ∼12 is determined by fitting both simulated $J_{{\rm sc}}$ and EQE to their experimental values, with a more accurate averaged reflectivity of the textured Al0.52In 0.48P/Au interface taken into account. Additionally, the measured open-circuit voltage ( $V_{{\rm oc}}$ ) is lower than the best achievable value due to the nonradiative recombination in the device, and a limited lifetime of ∼130 ns is determined by fitting the simulated and measured $V_{{\rm oc}}$ ; a specific series resistivity of 1.2 Ω·cm2 is determined to account for the 77.8% fill factor.

Ying-Shen Kuo

Papers

Ultra-thin GaAs single-junction solar cells integrated with a reflective back scattering layer

Stable p-type ZnO films grown by atomic layer deposition on GaAs substrates and treated by post-deposition rapid thermal annealing

Electrical and Optical Properties of n-Type Indium-Doped CdTe/Mg 0.46 Cd 0.54 Te Double Heterostructures

Ultra-thin GaAs single-junction solar cells integrated with an AlInP layer for reflective back scattering

Non-Lambertian Reflective Back Scattering and Its Impact on Device Performance of Ultrathin GaAs Single-Junction Solar Cells