Valence band offsets of the strained and longitudinally relaxed diamond/c-BN superlattices

The valence band offsets of the strained and longitudinally relaxed diamond/cubic boron-nitride （c-BN） （110） superlattice are investigated by the plane wave density functional theory approach and using the on-site core electron as a reference energy level. For the strained diamond/c-BN superlattice, the valence band offset of around 1.50 eV is in good agreement with those using all the electrons methods. As for the longitudinally relaxed superlattice, the valence band offset of around 1.28 eV is smaller than that of the strained superlattice. The reason for this is mainly due to the split of the valence band maximum caused by the anisotropic strain.

Study on Valence Band Offsets atStrained Heterojunctions

A method, which can predict the valence band offsets at strained layer heterojunctions under different strain situations only by calculating band structures and deformation parameters of the bulk materials, is suggested. The applicability of this method is verified by calculation of the valence band offsets at strained layer heterojuntions ,such as InP/InAs, InP/GaP, GaAs/InAs, GaP/GaAs and AlAs/InAs with various strain conditions.

Energy level engineering of charge selective contact and halide perovskite by modulating band offset:Mechanistic insights

Mixed cation and anion based perovskites solar cells exhibited enhanced stability under outdoor conditions,however,it yielded limited power conversion efficiency when TiO_(2) and Spiro-OMeTAD were employed as electron and hole transport layer(ETL/HTL)respectively.The inevitable interfacial recombination of charge carriers at ETL/perovskite and perovskite/HTL interface diminished the efficiency in planar(n-i-p)perovskite solar cells.By employing computational approach for uni-dimensional device simulator,the effect of band offset on charge recombination at both interfaces was investigated.We noted that it acquired cliff structure when the conduction band minimum of the ETL was lower than that of the perovskite,and thus maximized interfacial recombination.However,if the conduction band minimum of ETL is higher than perovskite,a spike structure is formed,which improve the performance of solar cell.An optimum value of conduction band offset allows to reach performance of 25.21%,with an open circuit voltage(VOC)of 1231 mV,a current density JSC of 24.57 mA/cm^(2) and a fill factor of 83.28%.Additionally,we found that beyond the optimum offset value,large spike structure could decrease the performance.With an optimized energy level of Spiro-OMeTAD and the thickness of mixed-perovskite layer performance of 26.56% can be attained.Our results demonstrate a detailed understanding about the energy level tuning between the charge selective layers and perovskite and how the improvement in PV performance can be achieved by adjusting the energy level offset.

Energy band alignment of PbTe/CdTe(111) interface determined by ultraviolet photoelectron spectra using synchrotron radiation

The energy band structure with type-I alignment at the PbTe/CdTe（111） heterojunction interface is determined by the ultraviolet photoelectron spectrum using synchrotron radiation. The valence band and conduction band offsets are obtained to be 0.09±0.12 and 1.19±0.12 eV, respectively. These results are in agreement with theoretically predicted ones. The accurate determination of the valence band and conduction band offsets is useful for the fundamental understanding of the mid-infrared light emission from the PbTe/CdTe heterostructures and its application in devices.

Band alignment of p-type oxide/ε-Ga2O3 heterojunctions investigated by x-ray photoelectron spectroscopy

Theε-Ga2O3 p-n heterojunctions(HJ)have been demonstrated using typical p-type oxide semiconductors(NiO or SnO).Theε-Ga2O3 thin film was heteroepitaxial grown by metal organic chemical vapor deposition(MOCVD)with three-step growth method.The polycrystalline SnO and NiO thin films were deposited on theε-Ga2O3 thin film by electron-beam evaporation and thermal oxidation,respectively.The valence band offsets(VBO)were determined by x-ray photoelectron spectroscopy(XPS)to be 2.17 eV at SnO/ε-Ga2O3 and 1.7 eV at NiO/ε-Ga2O3.Considering the bandgaps determined by ultraviolet-visible spectroscopy,the conduction band offsets(CBO)of 0.11 eV at SnO/ε-Ga2O3 and 0.44 eV at NiO/ε-Ga2O3 were obtained.The type-Ⅱband diagrams have been drawn for both p-n HJs.The results are useful to understand the electronic structures at theε-Ga2O3 p-n HJ interface,and design optoelectronic devices based onε-Ga2O3 with novel functionality and improved performance.

Ab initio Calculation of Valence-band Offsets for Lattice-matched Heterojunctions

In the light of our previous result that the average bond energy E_h valuelines up across heterojunction interfaces,in this paper,the valence-band offsets in ten hete-rojunctions have been calculated using the E_h as a reference level with the LMTO-ASAband-structure method.The calculated results are in excellent agreement with those fromthe more elaborate first-principles self-consistent interface calculations.As the presentmethod requires by far the smaller computational effort,it is very convenient for usingon medium-sized computers.

Valence offsets of ternary alloy heterojunctions In_xGa_(1-x)As/In_xAl_(1-x)As

The ternary alloy heterojunctions InxGa1-xAs/InxAl1-xAs are important materialswhich have been widely used in microwave and photoelectric devices.The alloy hetero-junctions InxGa1-xAs/InxAl1-xAs（x=0.3）have great potential use in high electron mobili-ty transistors（HEMTs）,heterostructure insulated-gate FFTs（HIGFETs）and resonant tun-neling diodes（RTDs）.When x rises to 0.53,InxGa1-xAs/InxAl1-xAs can be widely used inthe high-speed electronic devices.The valence-band offset（the value of ΔEv

多晶CdS/CdTe异质结界面的能带偏移

采用真空蒸发法制备了CdS和CdTe,并对其结构和光学性质进行了研究.原位制备了衬底沿(001)高度择优取向的CdS/CdTe异质结,研究了其结构、电子学性质.获得的CdS/CdTe半导体异质结的价带偏移ΔEV=0.98eV±0.05eV,导带偏移ΔEc=0.07±0.1eV.

三元合金异质结(AlP)_x(Si_2)_(1-x)/GaP和(GaP)_x(Si_2)_(1-x)/GaP的价带带阶

采用基于ＬＭＴＯＡＳＡ的平均键能计算方法和原子集团展开方法，研究了两组晶格匹配三元合金异质结（ＡｌＰ）ｘ（Ｓｉ２）１－ｘ／ＧａＰ和（ＧａＰ）ｘ（Ｓｉ２）１－ｘ／ＧａＰ的价带带阶ΔＥｖ（ｘ）值。研究表明，两组异质结的ΔＥｖ（ｘ）值随合金组分ｘ的变化都是非线性的，且表现出非单调的关系。

异质结价带边不连续△E_v理论计算中d态的作用

由半导体的LMTO能带计算平均健能E_1,并以平均键能E_1作为参考能级计算共阴离子异质结的△E值.在LMTO能带计算中采用不同处理d态的计算方法,系统地研究d态在△E,理论计算中的作用,研究结果表明,d态对主要能带的杂化程度显著地影响△E值;适当处理d态之后,以E为参考能级的△E计算方法可以得到接近于界面自洽方法(SCIC或SCSC)的准确结果。

AIN、GaN立方晶体的静态性质和AIN/GaN异质结的价带偏移

采用LMTO能带从头计算方法，计算了闪锌矿（立方）结构AIN和GaN的静态性质；用平均键能方法，预言了AlN与GaN自由应变生长、以AlN为衬底和以GaN为衬底等三种不同应变状态下AlN／GaN应变层异质结的△Ev值；最后，采用超原胞（AIN）n（GaN）n（001），（n=1，3，5）界面自洽计算方法，考察了超晶格中平均键能Em的“对齐”程度和验证了价带偏移△Ev计算结果的准确性。

掺碳锗硅合金最新研究进展

ＳｉＧｅＣ三元合金近几年来受到人们的广泛关注，碳的加入为Ｓｉ－Ｇｅ系统在能带和应变工程上提供了更大的灵活性。本文对碳加入锗硅材料中后应变的缓解及碳对合金能带结构的影响进行了概述，并对其机理做了总结。

合金异质结的价带带阶的计算方法

半导体异质结界面两侧价带带阶ΔE_v值(即va|ence-band offsets)是决定量子阱、超晶格电子态重要的物理量,无论是理论计算还是实验研究都具有重要的意义。

Si／Ge应变层异质结价带偏移的剪裁与设计

讨论应变层异质结价带偏移的剪裁、设计方法，研究Ｓｉ／Ｇｅ应变层异质结价带偏移设计参数与应变条件的关系，基于异质结中平均键能“对齐”，得到适用于Ｓｉ／Ｇｅ异质结价带偏移剪裁与设计的计算公式和图表。

Si/Ge应变层异质结的价带偏移理论计算

在应变异质结价带偏移从头算赝势法的理论计算中,建议一种以平均键能为参考能级的△E_v 值理论计算方法,该方法在以 Si 为衬底、以 Ge 为衬底和自由共度生长等3种不同应变情况的 Si/Ge 异质结价带偏移△E_v 值计算中,分别得到0.731eV、0.243eV 和0.521eV 的计算结果。

掺碳锗硅合金的制备及其性能研究进展

近几年来 Ｓｉ Ｇｅ Ｃ 三元合金受到人们的广泛关注，日益成为研究的热点之一。碳的加入为 Ｓｉ－ Ｇｅ 系统在能带和应变工程上提供了更大的灵活性。处于替代位置的碳能缓解 Ｓｉ Ｇｅ 合金的应变，并调节其能带。总结了碳的加入对锗硅材料中应变的缓解及碳对合金能带结构的影响，尤其是对弛豫状态下的锗硅材料及锗硅碳材料的调节作用。

多元合金异质结In_xGa_(1-x)As/In_xAl_(1-x)As的价带偏移

采用ＬＭＴＯ－ＡＳＡ能带计算方法，研究三元合金ＩｎｌＧａ４－ｌＡｓ４和ＩｎｌＡｌ４－ｌＡｓ４（ｌ＝０，１，２，３，４等五个有序态）的能带结构和平均键能Ｅｍ；在此基础上，将原子集团展开与平均键能方法结合起来计算了ＩｎｘＧａ１－ｘＡｓ／ＩｎｘＡｌ１－ｘＡｓ异质结的价带偏移ΔＥｖ（ｘ）值．研究表明：该异质结的ΔＥｖ（ｘ）值随合金组分ｘ的变化接近于线性；ΔＥｖ（ｘ）的理论计算值与实验结果相当符合．

应变异质结ZnSe/Si_2(110)的价带带阶的第一原理计算

本文从第一原理出发，用 Ｌｉｎｅａｒｉｚｅｄ－Ｍｕｆｆｉｎ－Ｔｉｎ（ＬＭＴＯ）能带方法对应变超晶格（ＺｎＳｅ）ｎ／（Ｓｉ２）。（１１０）（ｎ＝２～７）进行自洽计算．在此基础上采用冻结势方法计算了应变异质结ＺｎＳｅ／Ｓｉ２（１１０）的价带带阶，得到其理论值为 ０．９３ｅＶ，说明该异质结的价带带阶值较大，由其构成的量子阱对空穴运动有较强的限制作用．

应变层异质结ZnS/ZnSe的价带带阶

采用基于ＬＭＴＯ－ＡＳＡ的平均结合能计算方法，研究了在ＺｎＳｘＳｅ１－ｘ衬底上沿（００１）方向外延生长的应变层异质结ＺｎＳ／ＺｎＳｅ的价带带阶值。研究表明，应变的结果使价带带阶随衬底组分（ｘ）的变化呈非线性且单调的关系；与其他理论计算和实验结果比较。

三组三元合金异质结的价带带阶

采用基于LMTO－ASA的平均键能计算方法和原子集团展开方法，研究了三组典型的晶格匹配三元合金异质结（GaAs）x（Ge2）1-x／GaAs，（AlAs）x（Ge2）1-x／GaAs和AlxGa1-xAs／GaAs的价带带阶△Ev（x）值。研究表明：AlxGa1-xAs／GaAs异质结的Mv（x）值随合金组分x的变化接近于线性；（GaAs）x（Ge2）1-x／GaAs和（AlAs）x（Ge2）1-x／GaAs的△Ev（x）值随合金组分x的变化是非线性的。△Ev（x）的理论计算值与实验结果相当符合。