Multiple-wavelength emission from In/sub x/Ga/sub 1-x/As-GaAs quantum wells grown on a nanoscale faceted GaAs substrate by molecular beam epitaxy

Multiple-wavelength photoluminescence (PL) spanning a 160-nm range from 980 to 1140 nm (77 K) has been obtained from In/sub x/Ga/sub 1-x/As-GaAs quantum wells (QWs) with varying In composition x on a nanoscale faceted (nanofaceted) GaAs substrate grown by molecular beam epitaxy. Five nanofaceted regions which consist of periodic [100]-(n11) (n = 3 or 1) facets along [011~] with different periods were prepared on a single substrate by interferometric lithography and selective growth of GaAs. The pattern period p was varied from infinity (large-area unpatterned) to 210 nm while the lateral width of the (n11) facet region was kept constant at /spl sim/180 to 200 nm within each period. A 5-nm-thick In/sub 0.23/Ga/sub 0.77/As layer was deposited on this multiple-period nanofaceted single GaAs surface in a single-run growth. Orientation-dependent migration and incorporation (ODMI) of In atoms [mass transport of incident In atoms from the (n11) to adjacent [100] facets] results in a variation of x of the In/sub x/Ga/sub 1-x/As layer section on the [100] facet as the width of the [100] facet was changed from /spl sim/20 to /spl sim/200 nm. ODMI induces a higher x on the [100] facet for smaller p. The PL exhibits a polarization dependence which is more pronounced for decreasing p [i.e., the width of [100] facet]. Consistent variations of the PL peak energy and linear polarization along the pattern direction confirm that ODMI results in a variation of the In composition and imply that the In/sub x/Ga/sub 1-x/As layer on a [100] facet has characteristics of a quantum wire as its width is decreased to /spl sim/20 nm for p = 210 nm. A possible application of nanopatterned growth to wavelength-division-multiplexing transmitters is discussed.     

High-performance solar-blind photodetectors based on Al/sub x/Ga/sub 1-x/N heterostructures

Design, fabrication, and characterization of high-performance Al/sub x/Ga/sub 1-x/N-based photodetectors for solar-blind applications are reported. Al/sub x/Ga/sub 1-x/N heterostructures were designed for Schottky, p-i-n, and metal-semiconductor-metal (MSM) photodiodes. The solar-blind photodiode samples were fabricated using a microwave compatible fabrication process. The resulting devices exhibited extremely low dark currents. Below 3fA, leakage currents at 6-V reverse bias were measured on p-i-n samples. The excellent current-voltage (I--V) characteristics led to a detectivity performance of 4.9/spl times/10/sup 14/ cmHz/sup 1/2/W/sup -1/. The MSM devices exhibited photoconductive gain, while Schottky and p-i-n samples displayed 0.09 and 0.11 A/W peak responsivity values at 267 and 261 nm, respectively. A visible rejection of 2/spl times/10/sup 4/ was achieved with Schottky samples. High-speed measurements at 267 nm resulted in fast pulse responses with greater than gigahertz bandwidths. The fastest devices were MSM photodiodes with a maximum 3-dB bandwidth of 5.4 GHz.     

量子阱结构对GaInP/Ga(In)As/Ge电池的光谱响应改善

采用MOCVD工艺制备具有应变平衡量子阱结构GaInP/Ga(In)As/Ge三结太阳电池的方法,及量子阱结构对中间电池的光谱响应的改善,从而使GaInP/Ga(In)As/Ge三结太阳电池各子电池电流匹配设计更为合理,揭示了量子阱结构提高GaInP/Ga(In)As/Ge三结级联太阳电池光电转换效率的可能性。     

Numerical analysis of transmission coefficient,LDOS, and DOS in superlattice nanostructures of cubic $$\hbox {Al}_{x}\hbox {Ga}_{1-x}\hbox {N/GaN}$$ resonant tunneling MODFETs

Numerical analysis of the transmission coefficient, local density of states, and density of states in superlattice nanostructures of cubic \(\hbox {Al}_{x}\hbox {Ga}_{1-x}\hbox {N/GaN}\) resonant tunneling modulation-doped field-effect transistors (MODFETs) using \(\hbox {next}{} \mathbf{nano}^{3}\) software and the contact block reduction method is presented. This method is a variant of non-equilibrium Green’s function formalism, which has been integrated into the \(\hbox {next}\mathbf{nano}^{3}\) software package. Using this formalism in order to model any quantum devices and estimate their charge profiles by computing transmission coefficient, local density of states (LDOS) and density of states (DOS). This formalism can also be used to describe the quantum transport limit in ballistic devices very efficiently. In particular, we investigated the influences of the aluminum mole fraction and the thickness and width of the cubic \(\hbox {Al}_{x}\hbox {Ga}_{1-x}\hbox {N}\) on the transmission coefficient. The results of this work show that, for narrow width of 5 nm and low Al mole fraction of \(x = 20\,\%\) of barrier layers, cubic \(\hbox {Al}_{x}\hbox {Ga}_{1-x}\hbox {N/GaN}\) superlattice nanostructures with very high density of states of 407 \(\hbox {eV}^{-1}\) at the resonance energy are preferred to achieve the maximum transmission coefficient. We also calculated the local density of states of superlattice nanostructures of cubic \(\hbox {Al}_{x}\hbox {Ga}_{1-x}\hbox {N/GaN}\) to resolve the apparent contradiction between the structure and manufacturability of new-generation resonant tunneling MODFET devices for terahertz and high-power applications.     

MOCVD of Pb(Zr x Ti1-x )O3 thin films on MgTiO3/Si substrates and their electrical properties

Abstract

Pb(Zh _x , Ti_1-x )O₃(PZT) thin films were deposited on Si substrates using MgTiO₃ as the buffer layer and the electrical properties of those MFIS structures were investigated. PZT and MgTiO₃ films were made by MOCVD using ultrasonic spraying technique. Perovskite PZT films have been succesfully made at the substrate temperature of 550 to 600°C only when using MgTiO₃ buffer layer. AES depth profile analysis and RBS analysis revealed that there is no remarkable interdiffusion and no formation of reaction layer between PZT and MgTiO₃ and/or between MgTiO₃ and Si substrate. The capacitance-voltage (C-V) curves of the MFIS structure which were made with PZT and MgTiO₃buffer layer have shown the hysteresis resulted from the ferroelectric switching of the PZT films.     

Junctionless In0.3Ga0.7As/GaAs transistor with a shell doping profile for the design of a low-noise amplifier with a sub-1-dB noise figure for X-band applications

Journal of Computational Electronics - In this paper, a junctionless (JL) In0.3Ga0.7As/GaAs FET with a shell-doped channel (SDCh) for high-frequency electronics is investigated, and different...     

Mg2+掺参杂对LiFePO4/C结构和性能的影响

以乙酸镁为镁源,用LiOH·H2O、Fe(NO3)3·9H2O、NH4H2PO4为原料,通过水溶液法制备了掺杂Mg2+的LiFePO4/C正极材料.用XRD、SEM、恒流充放电测试、循环伏安(CV)和交流阻抗谱(EIS)方法,研究了Mg2+掺杂对LiFePO4/C的结构、形貌及电化学性能的影响.研究结果表明:Mg2+掺...     

Li与Ni+Co+Mn摩尔比对LixNi1/3Co1/3Mn1/3O2结构和性能的影响

采用氢氧化物共沉淀前驱体高温固相反应制备了层状LixNi1/3Co1/3Mn1/3O2(0.95≤x≤1.14)正极材料,应用ICP-OES、AAS对材料进行了成分分析,并采用X射线衍射光谱法(XRD)、晶格精修、扫描电子显微镜法(SEM)、差示扫描量热法(DSC)以及充放电测试表征了n(Li)∶n(Ni Co Mn)对材料结构和性能的影响。结果表明:x≥1.00时,随x值的增大,峰I003/I004的比值R、首次放电比容量及DSC峰值温度均呈现先增后减的趋势,并在x=1.05附近具有极大值;晶格精修表明阳离子混排率呈现先减后增的趋势,在x=1.08附近具有最小混排率。