A novel quantum directional coupler based on Pi-shaped coupled electron waveguides

We explore the possibility of a quantum directional coupler based on Pi-shaped coupled electron waveguides with smooth boundaries. By calculating the transmission spectra, we propose an optimized coupler structure with a high directivity and fine uniformity. The coupler specifications, directivity, uniformity, and coupling coefficient are evaluated.

Electrical properties of semi-insulating GaAs grown from the melt under microgravity conditions

A technologically important undoped semi-insulating (SI) GaAs single crystal was successfully grown in the Chinese recoverable satellite as far as we know for the first time by using a similar growth configuration described previously. The experimental results proved that the space SI GaAs crystals have a lower density of defects and defect-impurity complexes as well as a better uniformity.

An Improvement on 2× 2 Silicon-on-Insulator Mach-Zehnder Thermo-Optical Switch

An improved 2 ×2 silicon-on-insulator Mach-Zehnder thermo-optical switch is designed and fabricated, which is based on strongly guided multimode interference couplers and single- mode phase-shifting arms. The multimode interference couplers and input/output waveguides are deeply etched to improve coupler performances and coupler-waveguide coupling efficiencies. However, shallow etching is used in the phase-shifting arms to guarantee single-mode property. The strongly guided coupler presents an attractive uniformity about 0. 03 dB and a low propagation loss of -0.6 dB. The 2× 2 switch shows an insertion loss as low as -6.8 dB, where the fiber-waveguide coupling loss of -4.3 dB is included, and the response-time is measured as short as 6.8 μs, which are much better than our previous results.

X-Band GaN Power HEMTs with Power Density of 2.23W/mm Grown on Sapphire by MOCVD

The growth,fabrication,and characterization of 0.2μm gate-length AlGaN/GaN HEMTs,with a high mobility GaN thin layer as a channel,grown on (0001) sapphire substrates by MOCVD,are described.The unintentionally doped 2.5μm thick GaN epilayers grown with the same conditions as the GaN channel have a room temperature electron mobility of 741cm2/(V·s) at an electron concentration of 1.52×1016 cm-3.The resistivity of the thick GaN buffer layer is greater than 108Ω·cm at room temperature.The 50mm HEMT wafers grown on sapphire substrates show an average sheet resistance of 440.9Ω/□ with uniformity better than 96%.Devices of 0.2μm×40μm gate periphery exhibit a maximum extrinsic transconductance of 250mS/mm and a current gain cutoff frequency of77GHz.The AlGaN/GaN HEMTs with 0.8mm gate width display a total output power of 1.78W (2.23W/mm) and a linear gain of 13.3dB at 8GHz.The power devices also show a saturated current density as high as 1.07A/mm at a gate bias of 0.5V.

An Efficient MMI SOI Splitter with Multimode Input/Output Waveguides

A 1×8 multimode interference power splitter with multimode input/output waveguides in SOI material is designed by the beam propagation method and fabricated by the inductive coupled plasma etching technology for use in fiber optics communication systems.The fabricated device exhibits low loss and good coupling uniformity.The excess loss is lower than 0.8dB,and the uniformity is 0.45dB at the wavelength of 1550nm.Moreover,the polarization dependent loss is lower than 0.7dB at 1550nm.The device size is only 2mm×10mm.

Preparation of 50mm 3C-SiC/Si(111) as Substrates Suited for Ⅲ-Nitrides

50mm SiC films with high electrical uniformity are grown on Si(111) by a newly developed vertical low-pressure chemical vapor deposition (LPCVD) reactor.Both in-situ n- and p-type doping of 3C-SiC are achieved by intentional introduction of ammonia and boron into the precursor gases.The dependence of growth rate and surface morphology on the C/Si ratio and optimized growth conditions is obtained.The best electrical uniformity of 50mm 3C-SiC films obtained by non-contact sheet resistance measurement is ±2.58%.GaN films are grown atop the as-grown 3C-SiC/Si(111) layers using molecular beam epitaxy (MBE).The data of both X-ray diffraction and low temperature photoluminescence of GaN/3C-SiC/Si(111) show that 3C-SiC is an appropriate substrate or buffer layer for the growth of Ⅲ-nitrides on Si substrates with no cracks.

Non-stoichiometry Related Deep Level Defects in Semi-insulating InP

Semi-insulating (SI) InP materials have been prepared under different stoichiometric conditions, including Fe-doping in indium-rich melt and high temperature annealing undoped wafer in phosphorus and iron phosphide ambients. Deep level defects related with non-stoichiometry have been detected in the SI-InP samples. A close relationship between the material quality of electrical property and native deep defects has been revealed by a comprehensive study of defects in as-grown Fe-doped and annealed undoped SI-InP materials. Fe-doped SI-InP material with low carrier mobility and poor thermal stability contains a high concentration of deep defects with energy levels in the range of 0.1-0.4eV. The suppression of the defects by high temperature annealing undoped InP leads to the manufacture of high quality SI-InP with high mobility and good electrical uniformity. A technology for the growth of high quality SI-InP through stoichiometry control has been proposed based on the results.

Design and Fabrication of Ultracompact 3-dB MMI Coupler in Silicon-on-Insulator

An ultracompact 3-dB coupler is designed and fabricated in silicon-on-insulator,based on 12 line tapered multimode interference(MMI) coupler.Comparing with the conventional straigth MMI coupler,the device is-40% shorter in length.The device exhibits uniformity of 1.3dB and excess loss of 2.5dB

Multimode Interference Couplers with Different Background Refractive Index *

A novel structure of MMI coupler with different background refractive index has been designed. With stronger optical confinement in multimode waveguides, more guided modes are excited to improve imaging quality. Two-dimensional finite difference beam propagation method (2-D FDBPM) was used to simulate this new structure and had proven that its imaging quality, in terms of power uniformity and excess loss, is much better than conventional structure. This structure can be applied in SOI rib waveguides by deep etching method.

Temperature Dependence of Characteristics for Multimode Interference Based 3-dB Coupler in SOI

The temperature dependence of characteristics for multimode interference (MMI) based 3-dB coupler in silicon-on-insulator is analyzed, which originates from the relatively high thermo-optic coefficient of silicon. For restricted interference 3-dB MMI coupler, the output power uniformity is ideally 0 at room temperature and becomes 0. 32 dB when temperature rises up to 550 K. For symmetric interference 3-dB MMI coupler, the power uniformity keeps ideally 0 due to its intrinsic symmetric interference mechanism. With the temperature rising, the excess loss of the both devices increases. The performance deterioration due to temperature variety is more obvious to restricted interference MMI 3-dB coupler, comparing with that of symmetric interference MMI 3-dB coupler.

SOI Waveguides Fabricated by Wet-Etching Method

SOI waveguides fabricated by wet-etching method are demonstrated. The single mode waveguide and 1×2 3dB BBI splitter are analyzed and designed by three dimensional beam propagation method to correct the error of effective index method and guided mode method. The devices are fabricated. Excellent performances, such as low propagation loss of -1.37dB/cm, low excess of -2.2dB, and good uniformity of 0.3dB, are achieved.

Preparation of Semi-Insulating Material by Annealing Undoped InP

Semi-insulating (SI) InP wafers of 50 and 75mm in diameter can be obtained by annealing of undoped liquid encapsulated Czochralski (LEC) InP at 930 ℃ for 80h. The annealing ambient can be pure phosphorus (PP) or iron phosphide (IP). The IP-SI InP wafers have good electrical parameters and uniformity of whole wafer. However, PP-SI InP wafers exhibit poor uniformity and electrical parameters, Photoluminescence which is subtle to deep defect appears in IP-annealed semi-insulating InP. Traps in annealed SI InP are detected by the spectroscopy of photo-induced current transient. The results indicate that there are fewer traps in IP-annealed undoped SI InP than those in as-grown Fe-doped and PP-undoped SI-undoped SI InP. The formation mechanism of deep defects in annealed undoped InP is discussed.

Integrated tapered MMI couplers in the silicon-on-insulator technology

The authors have designed and fabricated 2x2 parabolically tapered MMI coupler with large cross-section and large space between difference ports using Silicon-on-Insulator ( SOI) technology. The devices demonstrate a minimum uniformity of 0.8dB and 30% shorter than the straight MMI coupler.

Thermodynamic analysis of GaSb-GaCl3 vapor phase epitaxy

A thermodynamic model for the GaSb-GaCl3 system in a closed quartz ampoule was proposed. The species in the gas phase are GaCl, GaCl3, Sb-4, Sb-2. The partial pressures of these species and total pressure in the ampoule have been calculated. The calculated results indicate that the equilibrium partial pressures of GaCl, GaCl3, Sb4, Sb2 and the total pressure in the ampoule have strong dependence on temperature, free volume inside the closed ampoule and amount of transport agent GaCl3. The total pressure will give strong influence not only on the flow pattern in the ampoule, but also on the uniformity of the epilayer.

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.