1.3 mu m GaInNAs/GaAs quantum well lasers and photodetectors

The growth of GalnNAs/GaAs quantum well (QW) has been investigated by solid-source molecular beam epitaxy (MBE). N was introduced by a dc-active plasma source. Highest N concentration of 2.6% in GaInNAs/GaAs QW was obtained, corresponding to the photoluminescence peak wavelength of 1.57 mum at 10K. The nitrogen incorporation behavior in MBE growth and the quality improvement of the QW have been studied in detail. 1.3 mum GaInNAs/GaAs SQW laser and MQW resonant-cavity enhanced photodetector have been achieved.

Selective intermixing of Ga(In)NAs/GaAs quantum well structures usingSiO(2) encapsulation and rapid thermal annealing

The quantum well intermixing of Ga(In)NAs/GaAs simple quantum well (SQW) using SiO2 encapsulation and rapid thermal annealing has been studied. Obvious enhanced intermixing of GaInNAs/GaAs SQW was observed due to the localized SiO2 capping layer and RTA at temperature between 650degreesC and 900degreesC. The selective intermixing strongly depends on N composition and In composition. An obvious selective intermixing had been found in the samples with small N composition and/or high In composition.

GaInNAs/GaAs quantum well lasers grown by solid-source molecular beam epitaxy

The growth of GaInNAs/GaAs quantum wells (QW) was investigated by solid-source molecular beam epitaxy. N was introduced by a dc-active plasma source. The effect of growth conditions such as on the N incorporation and photoluminescence (PL) intensity of the QWs has been studied. The PL peak intensity decreased and the PL fun width at half maximum increased with increasing N concentrations. The highest N concentration of 2.6% in a GaInNAs/GaAs QW was obtained, and corresponding to a PL peak wavelength of 1.57 mum at 10K. Rapid thermal annealing at 850degreesC significantly improved the crystal quality of the QWs. An optimum annealing time of 5s at 850degreesC was obtained. A GaInNAs/GaAs SQW laser with the emitting wavelength of 1.2 mum and a high characteristic temperature of 115 K was achieved at room temperature.

SiGe/Si quantum well resonant-cavity-enhanced photodetector

Resonant-cavity-enhanced photodetectors have been demonstrated to be able to improve the bandwidth-efficiency product. We report a novel SiGe/Si multiple quantum-well resonant-cavity-enhanced photodetector fabricated on a separation-by-implanted-oxygen wafer operating near 1300nm. The buried oxide layer in SIMOX is used as a bottom mirror to form a vertical cavity with silicon dioxide/silicon Bragg reflector deposited on the top surface. The quantum efficiency at the wavelength of 1300nm is measured with 3.5% at a reverse bias of 15V, which is enhanced by 10 folds compared with a conventional photodetector with the same absorption structures.

High power continuous-wave operation of self-organized In(Ga)As/GaAs quantum dot lasers

Quantum dot (QD) lasers are expected to have superior properties over conventional quantum well lasers due to a delta-function like density of states resulting from three dimensional quantum confinements. QD lasers can only be realized till significant improvements in uniformity of QDs with free of defects and increasing QD density as well in recent years. In this paper, we first briefly give a review on the techniques for preparing QDs, and emphasis on strain induced self-organized quantum dot growth. Secondly, self-organized In(Ga)As/GaAs, InAlAs/GaAlAs and InAs/InAlAs Qds grown on both GaAs and InP substrates with different orientations by using MBE and the Stranski-Krastanow (SK) growth mode at our labs are presented. Under optimizing the growth conditions such as growth temperature, V/III ratio, the amount of InAs, InxGa1-xAs, InxAl1-xAs coverage, the composition x etc., controlling the thickness of the strained layers, for example, just slightly larger than the critical thickness and choosing the substrate orientation or patterned substrates as well, the sheet density of ODs can reach as high as 10(11) cm(-2), and the dot size distribution is controlled to be less than 10% (see Fig. 1). Those are very important to obtain the lower threshold current density (J(th)) of the QD Laser. How to improve the dot lateral ordering and the dot vertical alignment for realizing lasing from the ground states of the QDs and further reducing the Jth Of the QD lasers are also described in detail. Thirdly based on the optimization of the band engineering design for QD laser and the structure geometry and growth conditions of QDs, a 1W continuous-wave (cw) laser operation of a single composite sheet or vertically coupled In(Ga)As quantum dots in a GaAs matrix (see Fig. 2) and a larger than 10W semiconductor laser module consisted nineteen QD laser diodes are demonstrated. The lifetime of the QD laser with an emitting wavelength around 960nm and 0.613W cw operation at room temperature is over than 3000 hrs, at this point the output power was only reduced to 0.83db. This is the best result as we know at moment. Finally the future trends and perspectives of the QD laser are also discussed.

Structural and optical properties of GaAsSb/GaAs heterostructure quantum wells

The structural and optical properties of MBE-grown GaAsSb/GaAs multiple quantum wells (MQWs) as well as strain-compensated GaAsSb/GaAs/GaAsP MQWs are investigated. The results of double crystal X-ray diffraction and reciprocal space mapping show that when strain-compensated layers are introduced, the interface quality of QW structure is remarkably improved, and the MQW structure containing GaAsSb layers with a high Sb composition can be coherently grown. Due to the influence of inserted GaAsP layers on the energy band and carrier distribution of QWs, the optical properties of GaAsSb/GaAs/GaAsP MQWs display a lot of features mainly characteristic of type-I QWs despite the type-II GaAsSb/GaAs interfaces exist in the structure. (C) 2004 Elsevier B.V. All rights reserved.

Controllable growth of semiconductor nanometer structures

Self-assembled quantum dots and wires were obtained in the InxGa1-xAs/GaAs and InAs/In0.52Al0.48As/InP systems, respectively, using molecular beam epitaxy (MBE). Uniformity in the distribution, density, and spatial ordering of the nanostructures can be controlled to some extent by adjusting and optimizing the MBE growth parameters. In addition, some interesting observation on the InAs wire alignment on InP(001) is discussed. (C) 2003 Elsevier Science Ltd. All rights reserved.

Transport properties through quantum dot in a vertical electric field

The transport properties through a quantum dot are calculated using the recursion method. The results show that the electric fields can move the conductive peaks along the high- and low-energies. The electric field changes the intensity of conductance slightly. Our theoretical results should be useful for researching and making low-dimensional semiconductor optoelectronic devices. (C) 2002 Elsevier Science B.V. All rights reserved.

Type-II SiGe/Si MQWS (multi-quantum wells) and self-organized Ge/Si islands grown by UHV/CVD system

Type-II SiGe/Si MQWs (Multi-Quantum Wells) and Self-Organized Ge/Si Islands were successfully grown by a homemade ultra-high vacuum/chemical vapor deposition (UHV/CVD) system. Growth characteristics and PL (photoluminescence) spectra at different temperature were measured. It demonstrated that some accumulation of carriers in the islands results in the increase of the integrated PL intensity of island-related at a certain temperature range.

Quantum computing

Quantum computing is a quickly growing research field. This article introduces the basic concepts of quantum computing, recent developments in quantum searching, and decoherence in a possible quantum dot realization.

Optical transitions and type-II band lineup of MBE-grown GaNAs/GaAs single-quantum-well structures

We have investigated transitions above and below band edge of GaNAs/GaAs and InGaNAs/GaAs single quantum wells (QWs) by photoluminescence (PL) as well as by absorption spectra via photovoltaic effects. The interband PL peak is observed to be dominant under high excitation intensity and at low temperature. The broad luminescence band below band edge due to the nitrogen-related potential fluctuations can be effectively suppressed by increasing indium incorporation into InGaNAs. In contrast to InGaNAs/GaAs QWs, the measured interband transition energy of GaNAs/GaAs QWs can be well fitted to the theoretical calculations if a type-II band lineup is assumed. (C) 2001 Elsevier Science B.V. All rights reserved.

Quality improvement of GaInNAs/GaAs quantum wells grown by plasma-assisted molecular beam epitaxy

The optimum growth condition of GaInNAs/GaAs quantum wells (QWs) by plasma-assisted molecular beam epitaxy was investigated. High-resolution X-ray diffraction and photoluminescence (PL) measurements showed that ion damage drastically degraded the quality of GaNAs and GaInNAs QWs and that ion removal magnets can effectively remove the excess ion damage. Remarkable improvement of PL intensity and obvious appearance of pendellosung fringes were observed by removing the N ions produced in the plasma cell. When the growth rate increased from 0.73 to 1.2 ML/s, the optimum growth temperature was raised from 460 degreesC to 480 degreesC and PL peak intensity increased two times. Although the N composition decreased with increasing growth rate, degradation of optical properties of GaInNAs QWs was observed when the growth rate was over 0.92 ML/s. Due to low-temperature growth of GaInNAs QWs, a distinctive reflection high-energy electron diffraction pattern was observed only when the GaAs barrier was grown under lower As-4 pressure. The samples with GaAs barriers grown under lower As-4 pressure (V/III ratio about 24) exhibited seven times increase in PL peak intensity compared with those grown under higher As-4 pressure (V/III ratio about 50). (C) 2001 Elsevier Science B,V. All rights reserved.

Modification of emission wavelength of self-assembled In(Ga)As/GaAs quantum dots covered by InxGa1-xAs(0 <= x <= 0.3) layer

Red shifts of emission wavelength of self-organized In(Cla)As/GaAs quantum dots (QDs) covered by 3 nm thick InxGa1-xAs layer with three different In mole fractions (x = 0.1, 0.2 and 0.3, respectively) have been observed. Transmission electron microscopy images demonstrate that the stress along growth direction in the InAs dots was reduced due to introducing the InxGa1-xAs (x = 0.1, 0.2 and 0.3) covering layer instead of GaAs layer. Atomic force microscopy pictures show a smoother surface of InAs islands covered by an In0.2Ga0.8As layer. It is explained by the calculations that the redshifts of the photoluminescence (PL) spectra from the QDs covered by the InxGa1-xAs (x greater than or equal to 0.1) layers were mainly due to the reducing of the strain other than the InAs/GaAs intermixing in the InAs QDs. The temperature dependent PL spectra further confirm that the InGaAs covering layer can effectively suppress the temperature sensitivity of PL emissions. 1.3 mum emission wavelength with a very narrow linewidth of 19.2 mcV at room temperature has been obtained successfully from In,In0.5Ga0.5As/GaAs self-assembled QDs covered by a 3-nm In0.2Ga0.2As strain reducing layer. (C) 2001 Elsevier Science B.V. All rights reserved.

Self-assembled quantum dots, wires and quantum-dot lasers

Molecular beam epitaxy-grown self-assembled In(Ga)As/GaAs and InAs/InAlAs/InP quantum dots (QDs) and quantum wires (QWRs) have been studied. By adjusting growth conditions, surprising alignment. preferential elongation, and pronounced sequential coalescence of dots and wires under specific condition are realized. The lateral ordering of QDs and the vertical anti-correlation of QWRs are theoretically discussed. Room-temperature (RT) continuous-wave (CW) lasing at the wavelength of 960 nm with output power of 3.6 W from both uncoated facets is achieved fi-om vertical coupled InAs/GaAs QDs ensemble. The RT threshold current density is 218 A/cm(2). A RT CW output power of 0.6 W/facet ensures at least 3570 h lasing (only drops 0.83 dB). (C) 2001 Elsevier Science B.V, All rights reserved.

Influence of substrate orientation on In0.5Ga0.5As/GaAs quantum dots grown by molecular beam epitaxy

In this paper, In0.5Ga0.5As quantum dots are fabricated on GaAs (100) and (n11)A/B (n = 3, 5) substrates by molecular beam epitaxy. Atomic force microscopy shows that the quantum dots on each oriented substrate are different in size, shape and distribution. In addition, photoluminescence spectra from these quantum dots are different in emission peak position, line width and integrated intensity. Auger electron spectra demonstrate that In concentration is larger near the surface than inside quantum dots, suggesting the occurrence of surface segregation effect during the growth of InGaAs dots. The surface segregation effect is found to be related to substrate orientation. (C) 2000 Elsevier Science B.V. All rights reserved.