Monolithic Integration of a Widely Tunable Laser with SOA Using Quantum-Well Intermixing

This paper presents an SG-DBR with a monolithically integrated SOA fabricated using quantum-well intermixing （QWI） for the first time in China's Mainland. The wavelength tuning range covers 33nm and the output power reaches 10mW with an SOA current of 50mA. The device can work at available channels with SMSR over 35dB.

4.3 THz quantum-well photodetectors with high detection sensitivity

We demonstrate a high performance GaAs/AlGaAs-based quantum-well photodetector(QWP)device with a peak response frequency of 4.3 THz.The negative differential resistance(NDR)phenomenon is found in the dark currentvoltage(I-V)curve in the current sweeping measurement mode,from which the breakdown voltage is determined.The photocurrent spectra and blackbody current responsivities at different voltages are measured.Based on the experimental data,the peak responsivity of 0.3 A/W(at 0.15 V,8 K)is derived,and the detection sensitivity is higher than 10^(11)Jones,which is in the similar level as that of the commercialized liquid-helium-cooled silicon bolometers.We attribute the high detection performance of the device to the small ohmic contact resistance of-2Ωand the big breakdown bias.

Stark Effect Dependence on Hydrogenic Impurities in GaAs Parabolic Quantum-Well Wires

The ground-state and lowest excited-state binding energies of a hydrogenic impurity in GaAs parabolic quantum-well wires （Q WWs） subjected to external electric and magnetic fields are investigated using the finite-difference method within the quasi-one-dimensional effective potential model. We define an effective radius Pen of a cylindrical QWW, which can describe the strength of the lateral confinement. For the ground state, the position of the largest probability density of electron in x-y plane is located at a point, while for the lowest excited state, is located on a circularity whose radius is Pen. The point and circularity are pushed along the left haft of the center axis of the quantum-well wire by the electric field dire ted along the right half. When an impurity is located at the point or within the circularity, the ground-state or lowest excited-state binding energies are the largest; when the impurity is apart from the point or circularity, the ground-state or lowest excited-state binding energies start to decrease.

Oxygen Scavenging Effect of LaLuO_3/TiN Gate Stack in High-Mobility Si/SiGe/SOI Quantum-Well Transistors

Higher-s dielectric LaLuO3, deposited by molecular beam deposition, with TiN as gate stack is integrated into high-mobility Si/SiGe/SOI quantum-well p-type metal-oxide-semiconduetor field effect transistors. Threshold voltage shift and capacitance equivalent thickness shrink are observed, resulting from oxygen scavenging effect in LaLuO3 with ti-rich TiN after high temperature annealing. The mechanism of oxygen scavenging and its potential for resistive memory applications are analyzed and discussed.

A low-threshold and high-power oxide-confined 850-nm AlInGaAs strained quantum-well vertical-cavity surface-emitting laser

A low-threshold and high-power oxide-confined 850-nm AlInGaAs strained quantum-well （QW） vertical-cavity surface-emitting laser （VCSEL） based on an intra-cavity contacted structure is fabricated. A threshold current of 1.5 mA for a 22 μm oxide aperture device is achieved, which corresponds to a threshold current density of 0.395 kA/cm2. The peak output optical power reaches 17.5 mW at an injection current of 30 mA at room temperature under pulsed opera- tion. While under continuous-wave （CW） operation, the maximum power attains 10.5 mW. Such a device demonstrates a high characteristic temperature of 327 K within a temperature range from -12°C to 96 °C and good reliability under a lifetime test. There is almost no decrease of the optical power when the device operates at a current of 5 mA at room temperature under the CW injection current.

Properties of Excitons Bound to Neutral Donors in GaAs-AlxGa1-xAs Quantum-Well Wires

In the effective-mass approximation, using a simple two-parameter wave function and a one-dimensional （ID） equivalent potential model, we calculate variationally the binding energy of an exciton bound to a neutral donor （D^0, X） in finite GaAs-AIxGa1-xAs quantum well wires （QWWs）. At the wire width of 25 A, the binding energy has a peak value, which is also at the position of the peak of the exciton binding energy, and the center-of-mass wave functions of excitons reaches the most centralized distribution. In addition, the changing tendency of the average interparticle distance as the wire width is reverse to that of the binding energy.

Co and Phthalocyanine Overlayers on the Quantum-Well System Co(001)/Cu: Spin-Polarized Electron Reflection Experiments

The influence of a Co or phthalocyanine (Pc) molecular overlayer on the properties of quantum-well resonances (QWR) in Cu layers atop Co(001) is studied by means of spin-polarized electron reflection. For Co atoms and Pc molecules, an energy shift of the QWR-induced signal is observed with increasing coverage and is attributed to a variation of the electron reflection phase at the Cu/Co and Cu/Pc interface. For Co we find a linear energy shift in the Cu QWR energy position with increasing coverage down to the sub-monolayer regime. This shows that the phase accumulation model remains accurate within the sub-monolayer regime of a discontinuous interface. An opposite sign in the energy shift between Co and Pc overlayers could reflect an opposite impact on the Cu surface work function of overlayer adsorption.

A New Process for Improving Performance of VCSELs

A new process method is proposed to improve the light output power of GaAs vertical cavity surface-emitting lasers （VCSELs）. The VCSELs with open-annulus-distributed holes have a light output power 1.34 times higher than those with ring trenches. The 14μm-aperture devices have a light output power higher than 10mW and have a maximum of 12.48mW at 29.6mA. In addition,open-annulus-distributed holes offer bridges for current injection,so the connecting Ti-Au metal between the ohmic contact and bonding pad does not have to cross the ring trench, and it therefore would not cause the connecting metal to be broken. These VCSELs also show high-temperature operation capabilities,and they have a maximum output power of 8mW even at an operation temperature of up to 60℃.

Excitonic Absorption of Semiconductor Nanorings under Terahertz Fields

The optical absorption of GaAs nanorings （NRs） under adc electric field and a terahertz （THz） ac electric field applied in the plane containing the NRs is investigated theoretically. The NRs may enclose some magnetic flux in the presence of a magnetic field perpendicular to the NRs plane. Numerical calculation shows that the excitonic effects are essential to correctly describe the optical absorption in NRs. The applied lateral THz electric field, as well as the dc field leads to reduction, broadening and splitting of the exciton peak. In contrast to the presence of a dc field, significant optical absorption peak arises below the zero-field bandgap in the presence ofa THz electric field at a certain frequency. The optical absorption spectrum depends evidently on the frequency and amplitude of the applied THz field and on the magnetic flux threading the NRs. This promises potential applications of NRs for magneto-optical and THz electro-optical sensing.

A Wavelength Tunable DBR Laser Integrated with an Electro-Absorption Modulator by a Combined Method of SAG and QWI

We report a wavelength tunable electro-absorption modulated DBR laser based on a combined method of SAG and QWI. The threshold current is 37mA and the output power at 100mA gain current is 3.5mW. When coupled to a single-mode fiber with a coupling efficiency of 15% ,more than a 20dB extinction ratio is observed over the change of EAM bias from 0 to -2V. The 4.4nm continuous wavelength tuning range covers 6 channels on a 100GHz grid for WDM telecommunications.

Ultraviolet and Deep-Ultraviolet Emissions from c-MgxZn1-xO/MgO Ultrathin Multilayer Heterostructures

Cubic phase MgxZn1-x O/MgO multilayer heterostructures （c-Mgx Zn1-xO/MgO MHs） are grown on Si（100） and quartz substrates by reactive electron beam evaporation at low temperature （250℃）. Cross-sectional morphology observations by field-emission scanning electron microscopy show the legible interfaces of c-MgxZn1-x O/MgO MHs. X-ray diffraction demonstrates that c-MgxZn1-xO/MgO MHs are of highly （100）-oriented. Optical trans- mission investigations of c-Mgx Zn1-x O/MgO MHs on quartz substrates reveal the coexistence of the two phases, c-MgxZn1-xO and MgO. Photoluminescence examination indicates the emergence of deep-ultraviolet emission centred at about 290nm along with the blue shift of the ultraviolet emission from 405nm to 39Gnm when the nominal thickness of c-MgxZn1-xO well layers of MHs is diminished to 3nm, which is probably originated from quantum confinement effect.

Non-Achievability of Metal-Insulator Transition in Two-Dimensional Systems

We present a simple demonstration of the nonfeasibility of metal-insulator transition in an exactly two-dimensional （2D） system. The Hartree-Fock potential in the 3D system is suitably modified and presented for the 2D case. The many body effects are included in the screening function, and binding energies of a donor are obtained as a function of impurity concentration so as to find out the possible way leading metal-insulator transition in the 2D system. While solving for the binding energy for a shallow donor in an isolated well of a GaAs/Ga1-x Als As superlattice system within the effective mass approximation, it leads to unphysical results for higher concentrations. It shows that the phase transition, the bound electron entering into the conduction band whereby （H）min=0, is not possible beyond this concentration. The results suggest thai a phase transition is impossible in 213 systems, supporting the scaling theory of localization. The results are compared with the existing data available and discussed in the light of existing literature.

Low-Threshold-Current and High-out-Power 660 nm Laser Diodes with a p-GaAs Current Blocking Layer for DVD-RAM/R

We investigate a new structure of high-power 660-nm AlGaInP laser diodes. In the structure, a p-GaAs layer is grown on the ridge waveguide serving as the current-blocking layer, and nonabsorbing windows are only fabricated near the cavity facets to increase the catastrophic-optical-damage level. Stable fundamental mode operation was achieved at up to 80roW without kinks, and the maximum output power was 184roW at 22~C. The threshold current was 40 mA.

Effect of Bias Step on the I-V Curve in Double-Barrier AlGaAs/GaAs/AlGaAs Resonant-Tunnelling Devices

We investigate the non-equilibrium electron transport properties of double-barrier AlGaAs/GaAs/AlGaAs resonant- tunnelling devices in nonlinear bias using the time-dependent simulation technique. It is found that the bias step of the external bias voltage applied on the device has an important effect on the final current-voltage （I - V） curves. The results show that different bias step applied on the device can change the bistability, hysteresis and current plateau structure of the I - V curve. The current plateau occurs only in the case of small bias step. As the bias step increases, this plateau structure disappears.

Characteristics of selective oxidation during the fabrication of vertical cavity surface emitting laser

Taking into account oxidation temperature, N2 carrier gas flow, and the geometry of the mesa structures this paper investigates the characteristics of selective oxidation during the fabrication of the vertical cavity surface emitting laser （VCSEL） in detail. Results show that the selective oxidation follows a law which differs from any reported in the literature. Below 435℃ selective oxidation of Al0.98Ga0.02As follows a linear growth law for the two mesa structures employed in VCSEL. Above 435℃ approximately increasing parabolic growth is found, which is influenced by the geometry of the mesa structures. Theoretical analysis on the difference between the two structures for the initial oxidation has been performed, which demonstrates that the geometry of the mesa structures does influence on the growth rate of oxide at higher temperatures.

Wavelength Tuning in the Two-Section Distributed Bragg Reflector Laser Fabricatedby Quantum-Well Intermixing

The two-section tunable ridge waveguide distributed Bragg reflector (DBR) lasers fabricated by strained In xGa1-xAsyP1-y The threshold current of the laser is 51mA. The tunable range of the laser is 3.2nm and the side mode suppression ratio (SMSR) is more than 38dB.

Enhancement of optical characteristic of InGaN/GaN multiple quantum-well structures by self-growing air voids

InGaN/GaN multiple quantum-well(MQW) structures with a wavelength range of green were successfully grown on a c-plane GaN template with SiO_2 stripe patterns along the [11-20] and [1-100] directions as a mask. The surface morphologies of both samples were investigated using scanning electron microscopy and demonstrated anisotropic growth characteristics of GaN. The optical characteristics were investigated using Raman spectra and photoluminescence(PL). The InGaN/GaN MQW structure grown on the GaN template with SiO_2 stripes along the [1-100] orientation exhibited less stress and higher PL intensity.Transmission electron microscopy results indicated that portions of MQWs were grown on an inclined semipolar plane, and air voids occurred only when the direction of the mask stripe was along the [1-100] orientation. The enhancement of the optical characteristic was due to the air-void structure and inclined semipolar quantum-well sidewalls.

Organic quantum-well characteristics of quasi-one-dimensional copolymers

Copolymers which are synthesized by oligomers or homopolymers have quasi-one-dimen sional structures. A tight-binding model was suggested to study the organic quantum-well properties of triblock copolymers xPA/nPPP/yPA and xPPP/nPA/yPPP consisting of polyacetylene (PA) and poly(p-phenylene) (PPP). It was found that the electronic density in the lowest conductive state ( LU MO) could be tuned by the ratios of homopolymers and interfacial coupling. The spontaneous quantum tunneling effects will occur in triblock copolymer xPA/nPPP/yPA with the increasing interfacial cou pling.

Quantum correlations and optical effects in a quantum-well cavity with a second-order nonlinearity

In this paper,we investigate the photon correlations and the statistical properties of light produced by an optical cavity with an embedded quantum well interacting with squeezed light.We show that the squeezed source substantially improves the intensity of the emitted light and generates a narrowing and a duplication of the spectrum peaks.With a strong dependence on frequency detuning,the cavity produces considerably squeezed radiation,and perfect squeezing is predicted for weak light–matter interactions.Furthermore,the system under consideration presents a bunching effect of the transmitted radiation resulting from weak pumping of the coherent field.The results obtained may have potential applications in the fields of very accurate measurement and quantum computing.

Slow and fast light in quantum-well and quantum-dot semiconductor optical amplifiers Invited Paper

Slow and fast light in quantum-well （QW） and quantum-dot （QD） semiconductor optical amplifiers （SOAs） using nonlinear quantum optical effects are presented. We demonstrate electrical and optical controls of fast light using the coherent population oscillation （CPO） and four wave mixing （FWM） in the gain regime of QW SOAs. We then consider the dependence on the wavelength and modal gain of the pump in QW SOAs. To enhance the tunable photonic delay of a single QW SOA, we explore a serial cascade of multiple amplifiers. A model for the number of QW SOAs in series with variable optical attenuation is developed and matched to the experimental data. We demonstrate the scaling law and the bandwidth control by using the serial cascade of multiple QW SOAs. Experimentally, we achieve a phase change of 160^o and a scaling factor of four at 1 GHz using the cascade of four QW SOAs. Finally, we investigate CPO and FWM slow and fast light of QD SOAs. The experiment shows that the bandwidth of the time delay as a function of the modulation frequency changes in the absorption and gain regimes due to the carrier-lifetime variation. The tunable phase shift in QD SOA is compared between the ground- and first excited-state transitions with different modal gains.