Q2D半导体电子和空穴统计

用半导体统计方法导出准二维半导体自由载流子面密度的数学表达式，并给出面密度与体密度之间关系式，采用维半导体自由载流子面密度表示式和范德堡－霍尔实验量在衬底GaAs上MBE生长的Q2D的样品GaSb和InAs和InAsi1-xSbx(x=0.22)禁带宽度Eg，获得满意结果。     

半导体技术

TN301 02050254Q ZD半导体电子和空穴统计/罗振华,吴仲埠(华东师范大学)“半导体情报.一2001,38(3)一52一55用半导体统计方法导出准二维半导体自由载流子面密度的数学表达式,并给出面密度与体密度之间关系式.采用二维半导体自由载流子面密度表示式和范德堡一霍尔实验测量在衬底G aAs上MBE生长的QZD的样品G asb和InA”卜二Sb二(x之0.22)禁带宽度E。,获得满意结果.图1参l(午)38(5),一44一47,57推导了在考虑了基区复合电流后双极晶体管厄利电压的理论表达式.用该表达式计算了Si/SIGe异质结双极晶体管的厄利电压,并且与仿真结果进行了…     

肖特基C-V法研究Al_xGa_(1-x)N/GaN异质结界面二维电子气

通过对 Pt/ Al0 .2 2 Ga0 .78N/ Ga N肖特基二极管的 C- V测量 ,研究分析了 Al0 .2 2 Ga0 .78N/ Ga N异质结界面二维电子气 (2 DEG)浓度及其空间分布 .测量结果表明 ,Al0 .2 2 Ga0 .78N/ Ga N异质结界面 2 DEG浓度峰值对应的深度在界面以下 1.3nm处 ,2 DEG分布峰的半高宽为 2 .3nm ,2 DEG面密度为 6 .5× 10 1 2 cm- 2 .与 Alx Ga1 - x As/ Ga As异质结相比 ,其 2 DEG面密度要高一个数量级 ,而空间分布则要窄一个数量级 .这主要归结于 Alx Ga1 - x N层中～ MV / cm量级的压电极化电场和自发极化电场对 Alx Ga1 - x N/ Ga N异质结能带的调制和 Alx Ga1 -     

1.55μm张应变InGaAsP/InGaAsP量子阱偏振不灵敏半导体光放大器的优化设计

优化设计了 1.5 5 μm In Ga As P/In Ga As P张应变量子阱偏振不灵敏半导体光放大器的结构 .利用 k· p方法计算了多量子阱的价带结构 ,计算中考虑了 6× 6有效质量哈密顿量 .从阱宽、应变、注入载流子密度等方面计算了量子阱模式增益的偏振相关性 .     

连续波工作高功率应变单量子阱半导体激光器

利用金属有机化合物气相淀积 ( MOCVD)技术成功生长了 In Ga As/Ga As/Al Ga As分别限制应变单量子阱材料 ,用该材料制成的单管半导体激光器在室温下连续波输出功率高达 2 .36 W,中心激射波长为 94 4nm,斜率效率高达 0 .96 W/A,阈值电流密度为 177.8A/cm2。该波长的半导体激光器是 Yb:YAG固体激光器的理想泵浦源。     

AlGaN/GaN异质结辐射感生界面态电荷对二维电子气输运的影响

根据荷电中心与自由载流子间的库仑散射作用,给出了异质结辐射感生界面态电荷对二维电子气(2DEG)迁移率的散射模型.计算了在不同沟道电子面密度下,界面态电荷密度与其所限制的迁移率之间的关系.运用马德森定则分析了辐射感生界面态电荷散射对总迁移率的影响.分析表明,辐射感生界面态电荷在累积到一定量后,会显著影响迁移率,一定程度上提高2DEG密度能抑制界面态电荷散射的作用     

AlGaN/GaN异质结辐射感生界面态电荷对二维电子气输运的影响

根据荷电中心与自由载流子间的库仑散射作用,给出了异质结辐射感生界面态电荷对二维电子气(2DEG)迁移率的散射模型.计算了在不同沟道电子面密度下,界面态电荷密度与其所限制的迁移率之间的关系.运用马德森定则分析了辐射感生界面态电荷散射对总迁移率的影响.分析表明,辐射感生界面态电荷在累积到一定量后,会显著影响迁移率,一定程度上提高2DEG密度能抑制界面态电荷散射的作用.     

双平面掺杂和单平面掺杂PHEMT器件的性能比较

研制了Al0 .2 4 Ga0 .76 As/ In0 .2 2 Ga0 .78As单平面掺杂PHEMT器件(SH - PHEMT)和双平面掺杂PHEMT器件(DH- PHEMT) ,并对其特性进行了比较.由于采用了双异质结、双平面掺杂的设计,DH- PHEMT能将载流子更好地限制在沟道中,得到更大的二维电子气浓度和更均匀的二维电子气分布,这些都有利于提高器件的性能.因此,DH- PHEMT器件具有更好的线性度,在较大的栅压范围内具有高的跨导和更大的电流驱动能力.这说明DH-PHEMT器件更加适用于高线性度应用的微波功率器件.     

大功率GRIN-SCH-SQW激光器阵列

分析了梯度折射率分别限制单量子阱 (GRIN-SCH-SQW)结构的特点以及对大功率半导体激光器特性的影响。利用分子束外延系统生长 Ga Al As/Ga As GRIN-SCH-SQW结构 ,经光荧光谱、X-射线双晶衍射、和载流子浓度测试 ,结果表明 ,该结构各参数均满足设计要求。应用此结构制成激光器阵列 ,室温准连续输出功率达5 8W(t=2 0 0 μs,f=5 0 Hz) ,峰值波长为 80 8nm。     

非对称异质波导半导体激光器结构

提出了一种非对称异质波导半导体激光器外延结构,即通过优化选择材料体系和结构厚度,对器件外延层的P侧限制结构和N侧限制结构分别设计,从而降低器件的电压损耗,使其满足高输出功率以及高的电光转换效率的要求.从载流子的输运和限制等微观机制出发,对器件的主要输出特性进行了理论分析和数值模拟,并以此为根据设计和制作了一种1060 nm In Ga As/Ga As单量子阱非对称异质波导结构半导体激光器,并对器件的主要输出特性进行了测试.实验结果表明,非对称异质结构是降低器件的电压降、增大限制结构对注入载流子的限制,提高半导体激光器电光转换效率的有效措施.     

Tailoring of Photoluminescence Properties in All-Vacuum Deposited Perovskite via Ruddlesden–Popper Faults

Ruddlesden–Popper (RP) faults are well known in oxide perovskites, and are also observed in promising metal halide perovskites. However, the effect of RP faults on optical properties of perovskite has not been systematically investigated. In this study, it is found that RP faults are common planar faults in all-vacuum deposited CsPbBr₃-based perovskite polycrystal thin films, and the density of RP planar faults can be greatly increased by non-stoichiometric composition (Cs-rich) as well as reduced dimensionality (quasi-2D) strategies. The photoluminescence (PL) measurement reveals monotonically increasing peak intensities with higher densities of RP planar faults from Cs-rich, quasi-2D to Cs-rich & quasi-2D samples. The corresponding atomic-scale differential phase contrast maps indicate strongly confined charges within the RP planar fault network, which explains well the relationship between PL enhancement and the density of RP planar faults, and offers an alternative pathway for tailoring the optoelectronic properties of perovskite.     

Double Charge Transfer Dominates in Carrier Localization in Low Bandgap Sites of Heterogeneous Lead Halide Perovskites

Heterogeneous organic-inorganic halide perovskites possess inherent non-uniformities in bandgap that are sometimes engineered and exploited on purpose, like in quasi-2D perovskites. In these systems, charge carrier and excitation energy migration to lower-bandgap sites are key processes governing luminescence. The question, which of them dominates in particular materials and under specific experimental conditions, still remains unanswered, especially when charge carriers comprise excitons. In this study transient absorption (TA) and transient photoluminescence (PL) techniques are combined to address the excited state dynamics in quasi-2D and other heterogeneous perovskite structures in broad temperature range, from room temperature down to 15 K. The data provide clear evidence that charge carrier transfer rather than energy migration dominates in heterogeneous quasi-2D perovskite films.     

Conductance of quasi-two-dimensional semiconductor systems with electrostatic disorder in the region of the percolation metal-insulator transition

Special features of the percolation transition in quasi-two-dimensional (quasi-2D) electron systems (metal-nitride-oxide-semiconductor structures with n-type inversion channels) with a strong fluctuation potential (FP) and a gate length smaller than the correlation radius of a percolation cluster (in which case the structure conductance is controlled by isolated saddle-point regions of the FP) are considered. Experimentally measured dependences of the conductance on the field-electrode potential and the temperature are analyzed in the context of the Landauer-Büttiker formalism. Energy parameters of the FP saddle-point regions and effective density of electron states (N _SS ∝ m/π?²) near the percolation level are determined from the experimental data. Consistency between the experimental results and the proposed statistical model of the formation of FP saddle-point regions in quasi-2D systems is demonstrated. It is shown that saddles transform into potential troughs extended in the direction of the percolation route as the percolation trough is approached.     

Side-Chain Functionalized Polymer Hole-Transporting Materials with Defect Passivation Effect for Highly Efficient Inverted Quasi-2D Perovskite Solar Cells

Compared with inverted 3D perovskite solar cell (PSCs), inverted quasi-2D PSCs have advantages in device stability, but the device efficiency is still lagging behind. Constructing polymer hole-transporting materials (HTMs) with passivation functions to improve the buried interface and crystallization properties of perovskite films is one of the effective strategies to improve the performance of inverted quasi-2D PSCs. Herein, two novel side-chain functionalized polymer HTMs containing methylthio-based passivation groups are designed, named PVCz-SMeTPA and PVCz-SMeDAD, for inverted quasi-2D PSCs. Benefited from the non-conjugated flexible backbone bearing functionalized side-chain groups, the polymer HTMs exhibit excellent film-forming properties, well-matched energy levels and improved charge mobility, which facilitates the charge extraction and transport between HTM and quasi-2D perovskite layer. More importantly, by introducing methylthio units, the polymer HTMs can enhance the contact and interactions with quasi-2D perovskite, and further passivating the buried interface defects and assisting the deposition of high-quality perovskite. Due to the suppressed interfacial non-radiative recombination, the inverted quasi-2D PSCs using PVCz-SMeTPA and PVCz-SMeDAD achieve impressive power conversion efficiency (PCE) of 21.41% and 20.63% with open-circuit voltage of 1.23 and 1.22 V, respectively. Furthermore, the PVCz-SMeTPA based inverted quasi-2D PSCs also exhibits negligible hysteresis and considerably improved thermal and long-term stability.     

Holy Water: Photo-Brightening in Quasi-2D Perovskite Films under Ambient Enables Highly Performing Light-Emitting Diodes

Quasi-2D perovskites provide new opportunities for lighting and display applications due to their high radiative recombination and excellent stability. However, seldom attention has been placed on their self-stability/working operation under ambient storage. Herein, quasi-2D perovskites/Polyethylene oxide (PEO) films are studied, showing an unforeseen photo-brightening effect under ambient storage (i.e., an increase of the photoluminescence quantum yield from 55% to 74% after 100 days). In stark contrast, those stored under a dark/inert atmosphere show a significant decrease down to 38%. This counterintuitive phenomenon responds to the increasing radiative recombination rate caused by the passivation of the surface Br vacancies in the presence of physically adsorbed water molecules, as corroborated by in situ/ex situ X-ray photoelectron spectroscopy and density functional theory calculations. Capitalizing on this surprising effect, stable light-emitting diodes (LEDs) using quasi-2D perovskites/PEO color filters are fabricated, realizing high stabilities of ≈400 h@10 mA under operating ambient conditions, representing a 20-fold enhancement compared to LEDs with 3D counter partners. Hence, this study reveals a unique insight into the impact of water passivation on the optical/structural properties of quasi-2D perovskite films, broadening their applications under operating ambient conditions.     

Efficient and Stable Quasi-2D Perovskite Solar Cells Enabled by Thermal-Aged Precursor Solution

Quasi-2D perovskites have received wide attention in photovoltaics owing to their excellent materials robustness and merits in the device stability. However, the highest power conversion efficiency (PCE) reported on quasi-2D perovskite solar cells (PSCs) still lags those of the 3D counterparts, mainly caused by the relatively high voltage loss. Here, a study is presented on the mitigation of voltage loss in quasi-2D PSCs via usage of thermal-aged precursor solutions (TAPSs). Based on the (AA)₂MA₄Pb₅I₁₆ (n = 5) quasi-2D perovskite absorber with a bandgap of ≈1.60 eV, a record-high open-circuit voltage of 1.24 V is obtained, resulting in boosting the PCE to 18.68%. The enhanced photovoltaic performance afforded by TAPS is attributed to the thermal-aged solution processing that triggers colloidal aggregations to reduce the nucleation sites inside the solution. As a result, formation of high-quality perovskite films featuring compact morphology, preferential crystal orientation, and lowered trap density is allowed. Of importance, with the improved film quality, the corrosion of Ag electrode induced by ion migrations is effectively restrained, which leads to a satisfactory storage stability with <2% degradation after 1200 h under nitrogen environment without encapsulation.     

Domain Distribution Management of Quasi-2D Perovskites toward High-Performance Blue Light-Emitting Diodes

Quasi-2D perovskites, as one of the promising materials applied in perovskite light-emitting diodes (PeLEDs), have attracted great attention for their superior semiconductor properties. The inherent multiquantum well structure can induce a strong confinement effect, which is especially suitable for blue emission. However, compared to their green counterparts, blue emitters constructed from quasi-2D perovskites are more sensitive to n domain distribution (where n represents the number of PbX₆ inorganic layers). Suffering from inefficient domain distribution management, blue PeLEDs now face a variety of negative issues, including color instability, multipeak emission, and poor fluorescence yield. In this review, the development of blue PeLEDs and the optical properties of quasi-2D perovskites are overviewed. Then, a classification and summary of strategies for domain distribution management are proposed. Finally, the challenges and potential directions of domain distribution management in quasi-2D perovskites are summarized. This review is expected to provide a comprehensive perspective and reference on domain distribution management toward efficient blue quasi-2D PeLEDs.     

Exciton Dynamics and Optically Pumped Lasing in 1-Naphthylmethylamine-Based Quasi-2D Perovskite Films

Films of the quasi-2D perovskite based on 1-naphthylmethylamine (NMA) are promising as the gain medium for optically pumped lasing and future electrically pumped lasing because of its low lasing threshold and small electroluminescence efficiency rolloff. However, reasons for the low threshold and small efficiency rolloff are still unclear. Therefore, exciton dynamics are investigated in NMA-based quasi-2D perovskite films. It is found that quenching of bright excitons by other excitons or charge carriers is unlikely in NMA-based quasi-2D perovskite films, which is one reason for the low lasing threshold and small efficiency rolloff. Moreover, thermally stimulated current measurements reveal that the defect levels inside the band gap of the NMA-based quasi-2D perovskite are shallow, with a depth of ≈0.3 eV, causing a decrease in nonradiative exciton recombination through the defects. Therefore, population inversion can be easily achieved, leading to the low lasing threshold as well. For fabrication of NMA-based quasi-2D perovskite laser devices with even lower lasing thresholds, a circular-shaped optical resonator, and small-molecule-based defect passivation are used. Optically pumped lasing can be obtained from these devices, with a threshold of ≈1 µJ cm⁻², which is one of the lowest values ever reported in any perovskite lasers.     

一种用于高压电平位移电路结构的准三维模拟方法

A new quasi-three-dimensional （quasi-3D） numeric simulation method for a high-voltage level-shifting circuit structure is proposed. The performances of the 3D structure are analyzed by combining some 2D device structures; the 2D devices are in two planes perpendicular to each other and to the surface of the semiconductor. In comparison with Davinci, the full 3D device simulation tool, the quasi-3D simulation method can give results for the potential and current distribution of the 3D high-voltage level-shifting circuit structure with appropriate accuracy and the total CPU time for simulation is significantly reduced. The quasi-3D simulation technique can be used in many cases with advantages such as saving computing time, making no demands on the high-end computer terminals, and being easy to operate.     

A quasi-3-dimensional simulation method for a high-voltage level-shifting circuit structure

A new quasi-three-dimensional (quasi-3D) numeric simulation method for a high-voltage level-shifting circuit structure is proposed. The performances of the 3D structure are analyzed by combining some 2D device structures; the 2D devices are in two planes perpendicular to each other and to the surface of the semiconductor. In comparison with Davinci, the full 3D device simulation tool, the quasi-3D simulation method can give results for the potential and current distribution of the 3D high-voltage level-shifting circuit structure with appropriate accuracy and the total CPU time for simulation is significantly reduced. The quasi-3D simulation technique can be used in many cases with advantages such as saving computing time, making no demands on the high-end computer terminals, and being easy to operate.