Temperature behavior of Franz-Keldysh oscillation and evaluation of interface electric fields attributed to strain effect of InAs/GaAs quantum dot

In this work, the electric field-induced Franz-Keldysh effect was used to investigate the localized electric fields in GaAs interfaces attributed to strain effect of InAs/GaAs quantum dots (QD). The electric fields were investigated by photoreflectance spectroscopy (PR). PR spectra of the InAs/GaAs QDs showed complex Franz-Keldysh oscillations (FKOs) with various temperatures. It is suggested that the FKOs originated from the interface electric fields predominately caused by the strain-induced polarization at GaAs interface near the InAs QDs. The InAs/GaAs QDs have a broad range of interface electric fields from ～10⁴ V/cm to ～2х10⁵ V/cm. Temperature behavior of FKO amplitude distribution is explained by temperature dependent carrier confinement effect.     

Theoretical modelling of XBn T2SLs InAs/InAsSb/B-AlAsSb mid-wave detector operating below thermoelectrical cooling

The paper reports on the barrier mid-wave infrared InAs/InAsSb (x_Sb = 0.4) type-II superlattice detector operating below thermoelectrical cooling. AlAsSb with Sb composition, x_Sb = 0.97; barrier doping, N_D < 2×10¹⁶ cm^?3 leading to valence band offset below 100 meV in relation to the active layer doping, N_D = 5×10¹⁵ cm^?3 was proved to be proper material not introducing extra barrier in valence band in the analyzed temperature range in XBn architectures. The detectivity of the simulated structure was assessed at the level of ～ 10¹¹ Jones at T ～ 100 K assuming absorber thickness, d = 3 μm. The detector’s architecture for high frequency response operation, τ_s = 420 ps (T ～ 77 K) was presented with a reduced active layer of d = 1 μm.     

Interband transitions and electronic properties of InAs/GaAs quantum dots embedded in AlxGa1−xAs/GaAs modulation-doped heterostructures

Reflection high-energy electron diffraction, atomic force microscopy, transmission electron microscopy, and double-crystal X-ray curves showed that high-quality InAs quantum dot (QD) arrays inserted into GaAs barriers were embedded in an Al_0.3Ga_0.7As/GaAs heterostructure. The temperature-dependent photoluminescence (PL) spectra of the InAs/GaAs QDs showed that the exciton peak corresponding interband transition from the ground electronic subband to the ground heavy-hole subband (E₁-HH₁) was dominantly observed and that the peak position and the full width at half maximum corresponding to the interband transitions of the PL spectrum were dependent on the temperature. The activation energy of the electrons confined in the InAs/GaAs QDs was 115 meV. The electronic subband energy and the energy wave function of the Al_0.3Ga_0.7As/GaAs heterostructures were calculated by using a self-consistent method. The electronic subband energies in the InAs/GaAs QDs were calculated by using a three-dimensional spatial plane wave method, and the value of the calculated (E₁-HH₁) transition in the InAs/GaAs QDs was in reasonable agreement with that obtained from the PL measurement.     

Interfaces as design tools for short-period InAs/GaSb type-II superlattices for mid-infrared detectors

The effect of interface anisotropy on the electronic structure of InAs/GaSb type-II superlattices is exploited in the design of thin-layer superlattices for mid-IR detection threshold. The design is based on a theoretical envelope function model that incorporates the change of anion and cation species across InAs/GaSb interfaces, in particular, across the preferred InSb interface. The model predicts that a given threshold can be reached for a range of superlattice periods with InAs and GaSb layers as thin as a few monolayers. Although the oscillator strengths are predicted to be larger for thinner period superlattices, the absorption coefficients are comparable because of the compensating effect of larger band widths. However, larger intervalence band separations for thinner-period samples should lead to longer minority electron Auger lifetimes and higher operating temperatures in p-type SLs. In addition, the hole masses for thinner-period samples are on the order the free-electron mass rather than being effectively infinite for the wider period samples. Therefore, holes should also contribute to photoresponse. A number of superlattices with periods ranging from 50.6 to 21.2 Å for the 4 μm detection threshold were grown by molecular beam epitaxy based on the model design. Low temperature photoluminescence and photoresponse spectra confirmed that the superlattice band gaps remained constant at 330 meV although the period changed by the factor of 2.5. Overall, the present study points to the importance of interfaces as a tool in the design and growth of thin superlattices for mid-IR detectors for room temperature operation.     

InAs和InAs/GaSb异质结的MOCVD生长和表征

以三甲基铟(TMIn)、砷烷(AsH3)、三甲基镓(TMGa)和三甲基锑(TMSb)为源,用水平常压MOCVD技术,在较低的Ⅴ/Ⅲ比的条件下(1.5～4)于GaAs和GaSb衬底上成功地生长了InAs合金和InAs/GaSb异质结。实验表明,生长温度在500℃～620℃范围内,InAs外延生长是扩散控制的。在Ⅴ/Ⅲ比为2.5时,生长效率(相对Ⅲ族源)为3×103μm/mol.不掺杂InAs外延层为n型的,室温迁移率为2000cm2/V.s.InAs/GaSb异质结的12KPL谱为一个在375meV处较宽的与杂质相关的跃迁峰,和一个在417meV附近的几乎被杂质峰湮没的带边峰.     

Fine structure of the exciton states in InAs quantum dots

The fine structure of the exciton states in InAs quantum dots grown by the Stranski-Krastanov method with short growth interruptions has been studied by microphotoluminescence at cryogenic temperatures. It has been demonstrated that, with increasing quantum-dot size, the splitting of the exciton states increases steadily to ～10² μeV. It has been shown that, in the exciton energy range of 1.3–1.4 eV, the magnitude of this splitting is comparable to the natural width of the exciton lines. This result is important for the development of entangled photon pair emitters based on InAs quantum dots.     

Investigation of populated InAs/GaAs quantum dots by photoluminescence and photoreflectance

We studied self-assembled InAs/GaAs quantum dots by contrasting photoluminescence and photoreflectance spectra from 10 K to room temperature. The photoluminescence spectral profiles comprise contributions from four equally separated energy levels of InAs quantum dots. The emission profiles involving ground state and excited states have different temperature evolution. Abnormal spectral narrowing occurred above 200 K. In the photoreflectance spectra, major features corresponding to the InAs wetting layer and GaAs layers were observed. Temperature dependences of spectral intensities of these spectral features indicate that they originate from different photon-induced modulation mechanisms. Considering interband transitions of quantum dots were observed in photoluminescence spectra and those of wetting layer were observed in photoreflectance profiles, we propose that quantum dot states of the system are occupied up to the fourth energy level which is below the wetting layer quantum state.     

Modeling tools for design of type-II superlattice photodetectors

In this paper, we present a range of modeling tools that are used in the design and performance evaluation of type-II superlattice detectors. Among these is an optical and photo carrier transport model for the spectral total external QE, which takes into account carrier diffusion length. Using this model, the diffusion length is extracted from external quantum efficiency measurements. It can also be used to fine-tune an optical cavity in relation to the wavelength range of interest for optimal quantum efficiency. Furthermore, an electrical device model for band bending, dark current and doping optimization is described. The modeling tools are discussed and examples of their use are given for MWIR type-II detectors based on InAs/AlSb/GaSb superlattices.     

Passivation techniques for InAs/GaSb strained layer superlattice detectors

InAs/(In,Ga)Sb Strained Layer Superlattices (SLSs) have made significant progress since they were first proposed as an infrared (IR) sensing material more than three decades ago. The basic material properties of SLS provide a prospective benefit in the realization of IR imagers with suppressed interband tunneling and Auger recombination processes, as well as high quantum efficiency and responsivity. With scaling of single pixel dimensions, the performance of focal plane arrays is strongly dependent on surface effects due to the large pixels’ surface/volume ratio. This article discusses the cause of surface leakage currents and various approaches of their reduction including dielectric passivation, passivation with organic materials (polyimide or various photoresists), passivation by overgrowth of wider bandgap material, and chalcogenide passivation. Performance of SLS detectors passivated by different techniques and operating in various regions of infrared spectrum has been compared.     

p型掺杂1.3μm InAs/GaAs量子点激光器的最大模式增益特性的研究

对p型掺杂13 μm InAs/GaAs量子点激光器的最大模式增益进行了实验和理论分析.实验上,测量了不同腔长激光器阈值电流密度与总损耗的对应关系,拟合出的最大模式增益为175 cm^-1,与相同结构非掺杂量子点激光器的最大模式增益一致.同时理论分析表明,p型掺杂对InAs/GaAs量子点激光器的最大模式增益并无影响,并且最大模式增益的计算结果与实验值相符.具有较小高度或高宽比的量子点能达到更高的最大模式增益,而较高的最大模式增益对p型掺杂13 μm InAs/GaAs自组织量子点激光器在光通信系统中的应用具有重要意义. 关键词： 最大模式增益 p型掺杂 InAs/GaAs量子点激光器     

Optical investigation of phosphorous-ion-implantation induced InAs/GaAs quantum dots' intermixing

This work reports on InAs/GaAs quantum dots (QDs) intermixing, induced by phosphorous ion implantation and subsequent rapid thermal annealing. The implantation process was carried out at room temperature at various doses (5×¹⁰¹⁰-¹⁰¹⁴ ions/cm²), where the ions were accelerated at 50 keV. To promote the atomic intermixing, implanted samples are subjected to rapid thermal annealing at 675 °C for 30 s. Low temperature photoluminescence (PL) measurements are carried out to investigate the influence of the interdiffusion process on the optical and electronic properties of the QDs. PL emission energy; linewidth and integrated intensity are found to exhibit a drastic dependence on the ion implantation doses. The band gap tuning limit has been achieved for an implantation dose of 5×¹⁰¹³ ions/cm². However, our measurement reveals that the accumulated defects for implantation doses higher than ¹⁰¹² ions/cm² drive the system towards the degradation of the QDs structure's quality.     

基于p-n结中反常光电转换现象的新型带间跃迁量子阱红外探测器

实验发现p-n结中局域载流子具有极高抽取效率,同时伴随着吸收系数的大幅度增加.本文报道上述现象的发现和验证过程,以及基于此现象的新型带间跃迁量子阱红外探测器(interband transition quantum well infrared detector,IQWIP)原型器件的性能.采用共振激发光致发光光谱技术,在InGaN量子阱、InGaAs量子阱、InAs量子点等多个材料体系中均观察到了在p-n结电场作用下的载流子高效逃逸现象,抽取效率分别为95%,87.5%,88%.利用含有InGaAs/GaAs多量子阱的PIN二极管,实验尝试了制备新型的IQWIP原型器件.在无表面减反射膜的实验条件下,利用仅100 nm的有效吸收厚度,实现了31%的外量子效率.基于这个数值推算得到量子阱的光吸收系数达到3.7×10~4cm~(-1),该数值高于传统透射实验测量体材料和量子阱结果.此外,还利用InAsSb/GaSb量子阱材料体系进行了2μm以上波长红外探测的探索.利用上述现象,有望在提高现有器件性能的同时开发出新颖的光-电转换器件.     

InAs/GaInSb超晶格薄膜结构与电学性能

采用分子束外延(MBE)方法, 调节生长温度、Ⅴ/Ⅲ束流比等参数在(001)GaAs衬底上生长了InAs/GaInSb超晶格薄膜.结果表明:InAs/GaInSb超晶格薄膜的最佳生长温度在385~395 ℃, Ⅴ/Ⅲ束流比为5.7 :1~8.7 :1.高能电子衍射仪(RHEED)原位观测到清晰的GaAs层(4×2)、GaSb层(1×3)和InAs层(1×2)再构衍射条纹.获得的超晶格薄膜结构质量较好.随着温度的升高, 材料的载流子浓度和迁移率均上升.     

Raman study of InAs/GaAs quantum dot solar cells

We report polarized and resonant Raman study of InAs/GaAs quantum dot solar cell (QDSC) structures. Raman spectra obtained from the top surfaces of the samples suggested that the formation of InAs QDs induced tensile strain in the overgrown GaAs layers. Furthermore, a longitudinal optical phonon-plasmon (LPP) coupled modes were observed in the p-type GaAs layers. The tensile strain was increased with an increase in the QD size. The hole concentrations estimated by fitting the individual LPP coupled modes were in the range of 2.4–3.5 × 10¹⁸ cm^?3. Resonant Raman spectra obtained from the cleaved sides, where the QDs were located, showed a 225 cm^?1 mode in parallel polarization configurations. Based on accurate analysis, this mode was identified as the LA(X) phonon of GaAs.     

脉冲激光原位辐照对InAs/GaAs(001)量子点生长的影响

在InAs/GaAs(001)量子点生长过程中, 当InAs沉积量为0.9 ML时, 利用紫外纳秒脉冲激光辐照浸润层表面, 由于高温下In原子的不稳定性, 激光诱导的原子脱附效应被放大, 样品表面出现了原子层移除和纳米孔. 原子力显微镜测试表明纳米孔呈现以[110]方向为长轴(尺寸: 20-50 nm)、[110]方向为短轴(尺寸: 15-40 nm)的表面椭圆开口形状, 孔的深度为0.5-3 nm. 纳米孔的密度与脉冲激光的能量密度正相关. 脉冲激光的辐照对量子点生长产生了显著的影响: 一方面由于纳米孔的表面自由能低, 沉积的InAs优先迁移到孔内, 纳米孔成为量子点优先成核的位置; 另一方面, 孔外的区域因为In原子的脱附, 量子点的成核被抑制. 由于带有纳米孔的浸润层表面具有类似于传统微纳加工技术制备的图形衬底对量子点选择性生长的功能, 该研究为量子点的可控生长提供了一种新的思路.     

Theoretical investigations of spin splittings in asymmetric AlSb/InAs/GaSb heterostructures and the possibility of electric field induced magnetization

We use the effective bond orbital model method to examine the spin splitting due to the Rashba effect in AlSb/InAs/GaSb asymmetric heterostructures. We find for the resulting two-dimensional electron gas (2DEG) under study that large theoretical values of the Bychkov–Rashba coefficients in the range of 30 × 10 ^{− 10}to 50 × 10 ^{− 10}eV · cm can be achieved. Finally, we present a phenomenon that might lead to a direct observation of the Rashba effect. We derive an expression, valid in the diffusive limit, for the spin polarization of the current resulting from a bias parallel to the plane of the quantum well.     

Hole mobility and remote scattering in strained InGaSb quantum well MOSFET channels with Al2O3 oxide

Hall mobility and major scattering mechanisms in surface and buried MBE grown strained InGaSb quantum well (QW) MOSFET channels with in‐situ grown Al₂O₃ gate oxide are analyzed as a function of sheet hole density, top‐barrier thickness and temperature. Mobility dependence on Al_0.8Ga_0.2Sb top‐barrier thickness shows that the relative contribution of interface‐related scattering is as low as ～30% in the surface QW channel. An InAs top capping layer reduces the interface scattering even further; the sample with 3 nm total top‐barrier thickness demonstrates mobility of 980 cm²/Vs giving sheet resistance of 4.3 kΩ/sq, very close to the minimum QW resistance in the bulk. The mobility–temperature dependences indicate that the interface‐related scattering is dominated by remote Coulomb scattering at hole densities <1 × 10¹² cm^–2. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Field induced interlayer interband coupled states in aperiodic InAs/GaSb heterostructures

The interlayer interband state coupling and the interfacial composition effect in aperiodic InAs/GaSb (001) heterostructures are studied with the scattering theoretic Green's function technique, which can handle interlayer multi-subband interaction under the external bias. The current density calculation shows that the interlayer interband coupled subbands enhance the peak current density by facilitating electron resonant tunneling. The calculated spectral local density of states of a heterostructure predicts that the GaAs interface shifts the energies of the quasibound states to lower energies than those of the InSb interface case, which agrees with experimental results.     

Method for determining the depleted zone thickness in silicon charged particle detectors

A method for determining the thickness of silicon charge particle detectors has been developed. The method is based on measurements of spectra from a standard ¹³⁷Cs γ source, whose shape changes with detector thickness. The method can be used in the thickness range ～50–6000 μm with an accuracy from 20 to 10%, respectively. No complex equipment or laborious calculations are needed.     

Modeling and simulation of long-wave infrared InAs/GaSb strained layer superlattice photodiodes with different passivants

Current–voltage characteristics of long-wave infrared (LWIR) InAs/GaSb strained layer superlattice photodiodes (cut-off wavelength ∼10 μm), passivated with different surface passivants, have been modeled and simulated using ATLAS software from SILVACO. The simulated results are fitted to previous experimental results obtained on unpassivated devices and those passivated by silicon-dioxide (SiO₂), silicon nitride (Si_xN_y) and zinc sulfide (ZnS). Surface parameters in terms of surface recombination velocity, shunt resistance and interface trap density are extracted for different passivants. The performance of silicon-dioxide passivated diode is solely dominated by a shunt leakage path with a shunt resistance value of 0.56 Ω-cm². Extracted electron and hole surface recombination velocities have values of 10⁵ cm/s and 10⁷ cm/s for unpassivated, 10³ cm/s and 10⁵ cm/s for Si_xN_y passivated and 10² cm/s and 10³ cm/s for ZnS passivated devices. Interface trap density follows a similar trend with values of 10¹⁵ cm⁻², 8.5 × 10¹⁴ cm⁻² and 10¹⁰ cm⁻² for unpassivated, Si_xN_y passivated and ZnS passivated devices respectively. The suitability and limitations of the simulation tool are discussed.