光和热诱导载流子的光电流谱比较研究

测量了包含有超薄层AlAs／GaAs超晶格的GaAs／AlGaAs多量子阱结构材料的光电流谱，比较研究了不同能级上的光和热诱导载流子在外电场下渡越超薄层AlAs势垒的隧穿时间，得到了光电导对外电场的依赖关系。     

量子点电致发光器件发光层能级变化与驱动电压的关系研究

以量子点电致发光器件(QLED)中能级分布和载流子浓度的关系为理论基础,研究了QLED发光层能级变化与驱动电压的关系,建立了数学模型.以CdSe/ZnS核壳结构量子点为发光层,计算了器件正常发光时的阈值电压,分析了电流密度与量子点中电子准费米能级与空穴准费米能级之差的关系.结果表明,当驱动电压大于9.8V时,CdSe/ZnS中电子的准费米能级与空穴的准费米能级之差大于1.03 eV,量子点电致发光器件正常发光;理论模型证实由于电子在发光层与电子传输层界面的大量积聚,导致淬灭发生,降低发光效率.     

锗硅量子阱异质界面附近缺陷研究

用深能级瞬态谱（ＤＬＴＳ）研究了量子阱样品价中载流子的热发射和异质界面附近的深能级缺陷，得到Ｓｉ０．６７Ｇｅ０．３３／Ｓｉ单量子样品的能带偏移为０．２４ｅＶ．量子阱异质界面附近高浓度的深能级缺陷在样品的ＤＬＴＳ谱上形成一少于峰，该信号只有当测量的脉冲宽度足够大时才能检测到．对比不；司组分相同结构的多量子阱样品发现，组分大时异质界面的深能级缺陷浓度大，因此它可能是失配应变或位错引起的．相应的光致发光谱（ＰＬ）测试结果表明该深能级缺陷还会导致ＰＬ谱中合金层的带边激子峰的湮灭．     

纳米硅量子点的自然形成及其发光特性

用 Si H4 气体的减压 CVD法 ,在氧化硅以及石英基板上自然形成了高密度的 (～ 10 11cm-2 )纳米尺寸的半球状硅晶粒 (硅量子点 ) ,并且对其光学吸收和发光 (Photo- luminescence,PL)特性进行了评价。用表面热氧化了的硅量子点样品 ,在室温条件且在高于 1.2 e V以上的能量范围内观察到了 PL谱。随着量子点尺寸的减少 ,PL谱的光学吸收限移向高能方向。 PL谱的峰值能呈现大幅度的 (约 0 .9e V)斯塔克移动 ,并且 PL谱的强度几乎与温度无关 ,说明发光来自与局域能级相关联的发光和复合过程。     

多孔硅上生长Ge量子点的光学特性

采用量子尺寸的多孔硅作为衬底 ,利用区域优先成核在多孔硅表面上成功地生长了 Ge量子点 .由于量子限制效应锗的 PL 谱发生了明显的蓝移 ,计算表明在傅里叶红外光谱中观察到的中红外 (5— 6 μm)吸收峰是源于量子点中的亚能带跃迁 (两个重空穴能级之间的跃迁 ) ,这为 Ge量子点红外光探测器的应用提供了理论基础     

多孔硅上生长Ge量子点的光学特性

采用量子尺寸的多孔硅作为衬底,利用区域优先成核在多孔硅表面上成功地生长了Ge量子点.由于量子限制效应锗的PL谱发生了明显的蓝移,计算表明在傅里叶红外光谱中观察到的中红外(5-6μm)吸收峰是源于量子点中的亚能带跃迁(两个重空穴能级之间的跃迁),这为Ge量子点红外光探测器的应用提供了理论基础.     

半导体锗纳米团簇和纳米层的生成与结构研究

我们在硅锗合金衬底上采用氧化等制膜方式生成零维和二维的纳米结构样品，用高精度椭偏仪(HPE)、卢瑟福背散射谱仪(RBS)和高分辨率扫描透射电子显微镜(HR-STEM)测量样品的纳米结构，并采用美国威思康新州立大学开发的Rump模拟软件对卢瑟福背散射谱(RBS)中的CHANNEL谱和RANDoM谱分别进行精细结构模拟，测量并计算出纳米氧化层与锗的纳米薄膜结构分布，并且反馈控制加工过程，优化硅锗半导体材料纳米结构样品的加工条件。我们测量出样品横断面锗纳米团簇和纳米层的PL发光谱。我们在硅锗合金的氧化层表面中首次发现纳米锗量子点组成的几个纳米厚的盖帽膜结构，我们首次提出的生成硅锗纳米结构的优化加工条件的氧化时间和氧化温度匹配公式的理论模型与实验结果拟合得很好。     

InGaAs/GaAs量子阱中自组装InAs量子点的光学性质

在InGaAs/GaAs量子阱中生长了两组InAs量子点样品,用扫描电子显微镜(SEM)测量发现,量子点呈棱状结构,而不是通常的金字塔结构,这是由多层结构的应力传递及InGaAs应变层的各向异性引起的.采用变温光致发光谱(TDPL)和时间分辨谱(TRPL)研究了其光致发光稳态和瞬态特性.研究发现,InGaAs量子阱层可以有效地缓冲InAs量子点中的应变,提高量子点的生长质量,可以在室温下探测到较强的发光峰.在量子阱中生长量子点可以获得室温下1 318 nm的发光,并且使其PL谱的半高宽减小到25 meV.     

量子阱红外探测器掺杂阱中能级的计算

量子阱中能级位置的确定是获得量子阱红外探测器其它设计参数的基础。为了提供足够的载流子跃迁,阱层一般为重掺杂层。重掺杂使半导体材料禁带宽度变窄,从而改变量子阱中能级的位置。通过对不同温度、量子阱区不同掺杂浓度条件下的量子阱材料PL 谱进行测量,得出PL 谱峰值波长对应的电子跃迁峰值能量,它与阱中基态能级的位置有关。分别计算了考虑和不考虑禁带变窄效应时的电子跃迁峰值能量,并与实验结果相比较,可以看出考虑禁带变窄效应时与实验结果相吻合,因此掺杂量子阱区能级的计算需要考虑禁带变窄效应,这样可以较为精确的得出阱中能级的位置。     

弛豫SiGe衬底上SiGe/SiⅡ型量子阱

采用 UHV / CVD系统 ,在 Si衬底上生长了具有渐变 Si1 - x Gex 缓冲层结构的弛豫 Si0 .76 Ge0 .2 4虚衬底和 5个周期的 Si0 .76 Ge0 .2 4/ Si多量子阱 .在渐变 Si1 - x Gex 缓冲层生长过程中引入原位退火 ,消除了残余应力 ,抑制了后续生长的 Si Ge中的位错成核 .透射电子显微照片显示 ,位错被有效地限制在组份渐变缓冲层内 ,而 Si Ge上层和 Si Ge/Si量子阱是无位错的 .在样品的 PL 谱中 ,观察到跃迁能量为 0 .96 1e V的 型量子阱的无声子参与 (NP)发光峰 .由于 型量子阱中电子和空穴不在空间同一位置 ,较高光功率激发下引起的高浓度载流子导致能带弯     

不对称双量子点系统中电压调控Kerr非线性增强

从理论上研究了不对称双量子点系统内的Kerr非线性增强效应。系统内量子点间的电压隧穿效应,可以在两个不同的探测频率位置同时诱导电磁感应透明。调节隧穿电压及控制光场可以改变吸收性质,从而得到其中一个透明窗口内无线性和非线性吸收的Kerr非线性增强效应。分析表明,量子点间的电压调控引起的隧穿是产生Kerr非线性增强的关键因素。     

Bias Voltage Controlled Memory Effect in In-Plane Quantum-Wire Transistors With Embedded Quantum Dots

The drain-current through GaAs/AlGaAs quantum-wire transistors (QWTs) with InGaAs quantum dots (QDs) exploited as floating gates is studied for temperatures up to 150 K. It is found that the threshold hysteresis between the up sweep and the down sweep of the gate voltage decreases with increasing bias voltage and is suppressed at a critical bias voltage. It is proposed and demonstrated that these QWTs show logic OR-gate functionality with the option to store the corresponding logic state by switching the bias voltage to zero. The authors explain this behavior by a bias voltage dependent efficiency of the gate to control differently the QDs and the quantum wire     

Coupling of electron states in the InAs/GaAs quantum dot molecule

Deep level transient spectroscopy (DLTS) is used to study electron emission from the states in the system of vertically correlated InAs quantum dots in the p-n InAs/GaAs heterostructures, in relation to the thickness of the GaAs spacer between the two layers of InAs quantum dots and to the reverse-bias voltage. It is established that, with the 100 Å GaAs spacer, the InAs/GaAs heterostructure manifests itself as a system of uncoupled quantum dots. The DLTS spectra of such structures exhibit two peaks that are defined by the ground state and the excited state of an individual quantum dot, with energy levels slightly shifted (by 1–2 eV), due to the Stark effect. For the InAs/GaAs heterostructure with two layers of InAs quantum dots separated by the 40 Å GaAs spacer, it is found that the quantum dots are in the molecule-type phase. Hybridization of the electron states of two closely located quantum dots results in the splitting of the levels into bonding and antibonding levels corresponding to the electron ground states and excited states of the 1s ⁺, 1s ^?, 2p ⁺, 2p ^?, and 3d ⁺ types. These states manifest themselves as five peaks in the DLTS spectra. For these quantum states, a large Stark shift of energy levels (10–40 meV) and crossing of the dependences of the energy on the electric field are observed. The structures with vertically correlated quantum dots are grown by molecular beam epitaxy, with self-assembling effects.     

两端联有铁磁电极的A-B环中的双量子点自旋极化输运

运用Keldysh格林函数方法,研究了两端联有铁磁电极的A-B环中的双量子点自旋极化输运.研究结果显示,系统的隧穿电流、自旋向上电流、自旋向下电流以及自旋累积明显的受自旋极化强度、外加电压和磁通的影响,并且随着极化强度的增大,在平行与反平行组态下的隧穿电流都减小,另外还出现了自旋分流现象.通过改变磁通,能明显地观察到两条通道的干涉现象.反平行组态下的自旋累积会随着极化强度的增大而增大.     

InAs自组织生长量子点的空穴俘获势垒

成功地用深能级瞬态谱（ＤＬＩＳ）研究了ｐ 型ＩｎＡｓ 自组织生长的量子点的电学性质,测得２．５ 原子层ＩｎＡｓ 量子点空穴基态能级在ＧａＡｓ 价带底上约０．０９ｅＶ,该量子点在荷电状态发生变化时需要克服一个势垒,俘获势垒高度为０．２６ｅＶ．本工作首次利用ＤＬＴＳ测定了量子点空穴的基态能级和俘获势垒,相信对增加量子点性质的理解会起到有益的帮助     

Localization of holes in an InAs/GaAs quantum-dot molecule

Deep-level transient spectroscopy is used to study the emission of holes from the states of a vertically coupled system of InAs quantum dots in p-n InAs/GaAs heterostructures. This emission was considered in relation to the thickness of a GaAs interlayer between two layers of InAs quantum dots and to the reversebias voltage U_r. It is established that hole localization at one of the quantum dots is observed for a quantum-dot molecule composed of two vertically coupled self-organized quantum dots in an InAS/GaAs heterostructure that has a 20-Å-thick or 40-Å-thick GaAs interlayer between two layers of InAs quantum dots. For a thickness of the GaAs interlayer equal to 100 Å, it is found that the two layers of quantum dots are incompletely coupled, which results in a redistribution of the hole localization between the upper and lower quantum dots as the voltage U_r applied to the structure is varied. The studied structures with vertically coupled quantum dots were grown by molecular-beam epitaxy using self-organization effects.     

双量子阱系统伏安特性的数值模拟

本文通过求解薛定谔方程得到由分段线性势垒构成的量子系统的变换矩阵和透射系数的精确解,并利用这一结果计算了双量子阱系统的偏压隧道电流,讨论了双量子阱系统结构变化对其伏安特性的影响。与单量子阱系统的比较表明,双量子阱系统在某些方面,如电流峰谷比,负微分电阻区等优于单量子阱系统。     

InAs自组织生长量子点的电子俘获势垒

成功地用深能级瞬态谱（ＤＬＴＳ）研究了ＩｎＡｓ自组织生长的量子点电学性质，获得２．５原子层ＩｎＡｓ量子点电子基态能级在ＧａＡｓ导带底下约０．１３ｅＶ，该量子点在荷电状态发生变化时伴随有晶格弛豫，对应俘获势垒为０．３２ｅＶ．本工作也证明可以把量子点类比深中心进行研究．     

有限深球方势阱研究Au纳米粒子自组装体系的I-V特性

本文在量子点的球方阱模型基础上，利用转移哈密顿法计算了纳米粒子自组装体系电子的跃迁几率，在此基础上，通过求解电子跃迁的主方程即可得到该体系的隧穿电流与偏压的关系。     

Broad-band photoresponse from InAs quantum dots embedded into InGaAs graded well

A broad-band photoresponse is obtained from undoped InAs multiple quantum dots grown by the molecular beam epitaxy (MBE) technique on a (100) GaAs substrate. The quantum dots were embedded in an In/sub x/Ga/sub 1-x/As graded well where the In mole fraction is chosen in the range of 0.3 /spl ges/ x /spl ges/ 0.0. The photoresponse of the reversed biased device, obtained at 80.5 K and using the normal incident configuration, was found to span the spectral range of 3.5 - 9.5 /spl mu/m. While the photoresponse is significantly high under the influence of the reverse bias voltage, the forward bias photoresponse is found to be negligible.