Impact of defects, buffer layer thickness, and substrate orientation on optical properties of epitaxial germanium

Fabrication of inverted bulk heterojunction organic solar cells based on conjugated P3HT:PCBM using various thicknesses of ZnO buffer layer

Stress evolution was studied in up to ~3 µm thick AlN templates, comprising ∼65 nm thick AlN nucleation layers (NLs) and thick buffer layers (BLs), grown using different growth modes and conditions by plasma-assisted molecular beam epitaxy (PA MBE) on c-Al2O3. Growth of both the NL and BL in a standard PA MBE mode at N-rich conditions (at flux ratio Al/N2* ∼ 0.5) led to instant generation of a relatively high tensile stress (∼1.5 GPa) which is maintained throughout the entire growth. On the contrary, NLs, grown using a migration-enhanced epitaxy (MEE), demonstrated a transition from the initial compressive stress to stress-free growth, which is usually observed in the Volmer–Weber films. Further growth of thick AlN BLs on the MEE–NLs at various Al/N2* ratios revealed a wide variety of stress evolution processes. The BL growth by using metal-modulated epitaxy (MME) at Me-rich conditions with Al/N2* ∼ 1.33 led to a gradual decrease in the initial compressive stress in the 2D AlN layers, whereas standard PA MBE growth of 3D BL at N-rich conditions (Al/N2* ∼ 0.92) exhibited a fast transition from the initial compressive stress to tensile stress. Moreover, we succeeded in achieving the quasi-stress-free growth of a 3.1 µm thick AlN BL using the MME growth mode at the optimum flux ratio Al/N2* = 1.05. These results were compared with the results of other authors and explained using a kinetic approach to description of stress evolution during PA MBE of AlN/c-Al2O3 templates, taking into account several simultaneously acting competitive mechanisms of continuous generation of tensile and compressive stresses.

The article discusses the magnetic and magnetoresistive properties of the [Co90Fe10/Cu]n multilayers prepared by magnetron sputtering as a function of the type of the substrate and the material and thickness of a buffer layer (Co90Fe10, Cu, Cr, Fe). The multilayers with a chromium buffer layer exhibit a sharp transition from low-coercive to high-coercive state at low variations in the thickness of the chromium layer (from 15 to 20 A). It has been demonstrated that the revealed sudden change in the hysteresis properties of the multilayers with a Cr buffer layer is accompanied by structural changes in the Cu and Co90Fe10 layers, characterized by the disappearance of the 〈111〉 texture at tCr > 20 A. It has been found that the most efficient buffer layer, which at room temperature ensures a threefold increase in the magnetoresistance at a minimum increase in hysteresis, is the Co90Fe10 (15 A) layer. It has been established that the substrate type ((100)Si, \((10\bar 12)\) Al2O3, glass) does not exert a significant effect on the magnetoresistive properties of the multilayers studied.

The role of a ZnO buffer layer in the growth of ZnO thin film on Al2O3 substrate

Growth and characteristics of ZnO films on growth side of freestanding diamond substrate dependent on buffer layer thickness

Dependence of optimum V/III ratio on substrate orientation, and influence of buffer layer on MOVPE grown InSb/GaSb quantum dots

Growth of crystalline quartz films with AT-cut plane by means of catalyst-enhanced vapor-phase epitaxy under atmospheric pressure

Cu(In,Ga)Se 2 (CIGS) thin films were deposited on Molybdenum coated soda lime glass (SLG/Mo) substrates, using physical vapor deposition (PVD) 3-stage process. The CIGS films were treated by ammonium hydroxide solution before depositing the I-ZnO buffer layer. The I-ZnO layer was deposited using metallorganic chemical vapor deposition (MOCVD) at different substrate temperatures of 200°C, 250°C, and 300°C. The thickness of this buffer layer was varied according to the location of the substrates with respect to the gas flow direction. The CIGS devices were completed by depositing the Al-ZnO window layer by rf magnetron sputtering and applying the Ni/Al front contact grids. The thickness of the I-ZnO buffer layer was measured using a Dek-tak profilometer on soda lime glass substrates which were used as reference samples during the deposition process of I-ZnO buffer layer on CIGS films. Surface depth profiling survey for the elements and their chemical states, as well as their relative concentration was analyzed by X-Ray Photoelectron Spectroscopy (XPS) for as deposited and ammonium hydroxide treated CIGS films. In addition, the performance of the completed CIGS devices was evaluated under standard conditions of 1000 W/m2 and 25°C.

The crystal structure and hysteresis properties of FeNi/NiMn/FeNi multilayer films with varying composition of the NiMn layer (9, 27, and 49 at % Ni) and the thickness of the FeNi buffer layer (50–400 A) preceding the NiMn layer are studied. In the films that have NiMn layers with 9 at % Ni, exchange bias is observed only in the lower layer, while in the films with 27 at % Ni, exchange bias is observed in both permalloy layers. It is established that the exchange bias field depends on the thickness of the buffer layer, and on the position of the permalloy layer in a film.

An Al doped ZnO (ZnO:Al) transparent thin film transistors (TTFTs) with various thickness of ZnO buffer layer sandwiched between gate insulator and channel ayer were deposited by a magnetron radio frequency co-sputter system. When the thickness of the buffer layer was 80 nm, the field-effect carrier mobility of the TTFTs was as high as 122.0 cm^2/V-s. Furthermore, the associated gate voltage swing was 0.24 V/decade, and the maximum state density was 2.69×10^11 eV^−1cm^−2. The on-to-off current ratio of the TTFTs with 80 nm-thick ZnO buffer layer was up to 5×10^7.

본 논문에서는 버퍼막 두께 및 열처리 온도에 따른 ZnO/b-ZnO/p-Si(111) 기반 이종접합 다이오드 전류 특성에 대한 연구가 진행되었고, b-ZnO (ZnO buffer layer) 버퍼막 두께 및 열처리 온도에 따른 p-Si(111) 기판 위에 증착시킨 ZnO 박막의 구조적, 전기적 특성 또한 연구되었다. X-ray diffraction (XRD) 방법을 이용하여 ZnO 박막의 구조적 특성을 측정하였고, semiconductor parameter analyzer를 이용하여 ZnO/b-ZnO/p-Si(111) 이종접합 다이오드의 I-V 특성을 평가하였다. XRD 분석 결과 버퍼막 열처리 온도 <TEX>$700^{\circ}C$</TEX>, 버퍼막 두께 70 nm에서 ZnO 박막은 우세한 (002) 방향의 c-축 배향성을 갖는 육방정계(hexagonal wurtize) 결정 구조를 나타내었다. 전기적 특성인 운반자 농도, 비저항 값의 경우에는 버퍼막 열처리 온도 <TEX>$700^{\circ}C$</TEX>, 버퍼막 두께 50 nm에서 우수한 전기적 특성(비저항: <TEX>$2.58{\times}10^{-4}[{\Omega}-cm]$</TEX>, 운반자 농도: <TEX>$1.16{\times}10^{20}[cm^{-3}]$</TEX>)을 보였다. 또한 ZnO/b-ZnO/p-Si(111) 이종접합 다이오드의 전류 특성은 버퍼막 열처리 온도 <TEX>$700^{\circ}C$</TEX>에서 버퍼막 두께가 증가할수록 전류 특성이 향상되는 경향을 보였다. In this study, the effects of ZnO buffer layer thickness and annealing temperature on the heterojunction diode, ZnO/b-ZnO/p-Si(111), were reported. The effects of those on the structural and electrical properties of zinc oxide (ZnO) films on ZnO buffered p-Si (111) substrate were also studied. Structural properties of ZnO thin films were studied by X-ray diffraction and I-V characteristics were measured by a semiconductor parameter analyzer. ZnO thin films with 70 nm thick buffer layer and annealing temperature of <TEX>$700^{\circ}C$</TEX> showed the best c-axis preferred orientation. The best electrical property was found at the condition of buffer layer annealing temperature of <TEX>$700^{\circ}C$</TEX> and 50nm thick ZnO buffer layer (resistivity: <TEX>$2.58{\times}10^{-4}[{\Omega}-cm]$</TEX>, carrier concentration: <TEX>$1.16{\times}1020[cm^{-3}]$</TEX>). The I-V characteristics for ZnO/b-ZnO/p-Si(111) heterojunction diode were improved with increasing buffer layer thickness at buffer layer annealing temperature of <TEX>$700^{\circ}C$</TEX>.

Raman spectroscopy was used to study the band bending at the interface of ZnSe/GaAs hetero‐structures. A series of samples, which contained a ZnSe buffer layer, 0–35 nm thick, grown at a lower temperature than the much thicker ZnSe epilayer, by metal–organic chemical vapor phase deposition, were investigated. Compared with that of the GaAs substrate, an enhancement of the intensity of the LOGaAs phonon was found in samples grown without and with a thick (≥28 nm) buffer layer, but not in a sample grown with a 4 nm thick buffer layer. The enhancement is attributed to the electric field induced Raman scattering, resulted from a strong band bending on the GaAs side of the hetero‐structure. The results suggest that the direction of the interfacial electric field on the GaAs side will reverse with increasing buffer layer thickness. Between this reversal, a near flat band condition can be achieved, as was found in a sample grown with a 4 nm buffer layer. This suggestion is consistent with the concomitant improvement of the structure of the epilayer and of the interfacial quality of the hetero‐junction, which unpins the Fermi level and affects the band bending. Copyright © 2001 John Wiley &amp; Sons, Ltd.

The effect of multivalent defect density, thickness of absorber and buffer layer thickness on the performance of CIGS solar cells were investigated systematically. The study was carried out using Solar Cells Capacitance Simulator (SCAPS) code, which is capable of solving the basic semiconductor equations. Employing numerical modelling, a solar cell with the structure Al|ZnO : Al|In2S3|CIGS|Pt was simulated and in it, a double acceptor defect (-2/-1/0) with a density of 1014 cm-3 was set in the absorber in the first instance. This initial device gave a power conversion efficiency (PCE) of 25.85 %, short circuit current density (Jsc) of 37.9576 mAcm-2, Photovoltage (Voc) of 0.7992 V and fill factor (FF) of 85.22 %. When the density of multivalent defect (-2/-1/0) was varied between 1010 cm-3 and 1017 cm-3 the solar cells performance dropped from 26.81 % to 16.87 %. The champion device was with multivalent defect of 1010 cm-3 which shows an enhancement of 3.71 % from the pristine device. On varying the CIGS layer thickness from 0.4 um to 3.6 um, an increase in PCE was observed from 0.4 um to 1.2 um then the PCE began to decrease beyond a thickness of 1.2 um. The best PCE was recorded with thickness of 1.2 um which gave Jsc of 37.7506 mAcm-2, Voc of 0.8059 V, FF of 85.2655 %. On varying the In2S3 (buffer) layer thickness from 0.01 um to 0.08 um, we observed that there was no significant change in photovoltaic parameters of the solar cells as buffer layer thickness increased.

Effects of buffer layer thickness on properties of ZnO thin films grown on porous silicon by plasma-assisted molecular beam epitaxy

Background/Objectives: In this article the buffer materials, α-6T and α-7T are used to study the interface of metla/organic in OLEDs. It has been observed that the electrical, light emitting and efficiency properties are strongly depend on the thickness of the buffer layer with 60nm of α-6T and 3nm of α-7T the mostly improved properties were observed. Methods/Statistical analysis: The physical interaction of molecular at the metal/organic interface has been investigated by contact angle hysteresis. The surface energy of oligothiophene layer on ITO electrode varies within 10mJ/cm2. The polar component of surface energy of organic materials(HTL) on buffer layer materials was observed to be independent on the thickness of buffer layer with the value of zero. The strong electrostatic force of the metallic surface may lead the properties of organic materials to be different from that of natural state. However the buffer layer may contribute to the continuously layered similar energy state that increase the efficiency of hole injection. Findings: It has been observed that the electrical properties, light emitting and efficiency properties are strongly depend on the thickness of the buffer layer with 60nm of α-6T and 3nm of α-7T the mostly improved properties were observed. The lowered energy barrier, about 0.2 ~ 0.4eV, for hole injection at the interface of metal/buffer layer and the improved surface morphology of hole injection surface may contribute to the improvements. It was expected that the increase of the absolute number of holes injected might increase the light emitting efficiency and it was observed. Improvements/Applications: As a tool to investigate such as phenomena, the use of buffer materials gives advantages. The buffer materials normally show stable chemical and physical properties, it could be avoided the destruction of original electronic state during the measurement. The use of buffer materials and the understandings of interface phenomena could offer many applicable products to our common life.