微光电子集成灵巧象素器件

我们采用 MBE生长出大周期 Ga As/ Al Ga As多量子阱 (MQW)外延材料 ,研制了适用于倒装焊结构的自电光效应器件 (SEED)列阵 ,并与 Si CMOS电路通过倒装焊工艺集成为微光电子集成灵巧象素器件。通过对光电特性测试表明 ,器件具有良好的光探测和光调制性能。     

20 dB contrast GaAs/AlGaAs multiple quantum-well nonresonantmodulators

The authors report a successful fabrication of nonresonant GaAs/AlGaAs multiple quantum well (MQW) modulators with a contrast ratio of more than 20 dB and a wide bandwidth of 3 nm. The optical path, as long as 8 μm, is attained by fabricating a high-purity thick MQW layer with a residual carrier concentration of less than 10¹⁴ cm^-3 and introducing a high-reflectivity AlAs/AlGaAs quarter-wavelength mirror. The driving wavelengths are located at the absorption edge, resulting in the low-absorption loss     

Pair-groove-substrate GaAs/AlGaAs multiquantum-well lasers with a self-aligned stripe geometry

GaAs/AlGaAs multiquantum-well (MQW) lasers with a self-aligned structure incorporating a waveguide and current confinement were fabricated on a substrate with a pair of etched grooves using two-step epitaxial growth. First, a current-blocking layer was grown selectively on the substrate by low-pressure organometallic vapour-phase epitaxy (OMVPE), and then the GaAs/AlGaAs MQW laser structure was constructed on the substrate with the OMVPE layer by molecular-beam epitaxy. The mesa-shaped part of the active layer above the current-confinement region provides a lateral refractive-index optical waveguide. The lasers show well controlled transverse-mode oscillations with low threshold currents.     

Dielectric properties of GaAs AlGaAs multiple quantum well waveguides

GaAs/AlGaAs multiple quantum well (MQW) waveguides are investigated using the grating coupling technique. Large polarization dependent effects of the two-dimensional excitons are seen in the TE/TM dispersion relation of single mode slab waveguides. By treating the MQW as a layered composite dielectric, we deduce the oscillator strengths of the heavy and light hole excitons, and the background dielectric constant of the MQW without the excitonic contribution, for fields polarized parallel and perpendicular to the MQW layers.     

1 Gbit/s automatic-power-control-free zero-bias modulation of very-low threshold MQW laser diodes

The first 1 Gbit/s, automatic-power-control-free zero-bias modulation has been successfully demonstrated using very low-threshold GaAs/AlGaAs MQW lasers. A stable multi-longitudinal mode oscillation due to zero-bias modulation was also observed. This result simplifies driving circuitry and is an important step towards realisation of high-speed and high-density optoelectronic integrated circuits.     

Multiple quantum well PIN optoelectronic devices and a method of restoring failed device characteristics

Multiple quantum well (MQW) optical modulators have a wide range of applications in fiber-optic and remote communication systems. One of the challenges in producing reliable devices is maintaining the necessary PIN electrical characteristics while having large areas of complex MQW structures for optical processing. We report the first direct correlation between crystalline material imperfections and reverse bias behavior in MQW PIN devices. Molecular beam epitaxy grown GaAs/AlGaAs and strained InGaAs/AlGaAs MQW PIN structures are examined. Defects originating in the epitaxial material provide a conducting path along the PIN junction degrading the device performance and lowering the yield. Defectectomy, a method of eliminating the crystalline defects and restoring the device characteristics and improving the yield is described.     

Effect of GaAs/AlGaAs quantum-well structure on refractive index

We investigate the refractive index difference between the GaAs/AlGaAs quantum wells (QWs) and bulk AlGaAs. We find the refractive index difference is smaller when the electric field in the nominally intrinsic MQW region is larger, or when the well (GaAs) thickness of the QW's is larger, or when the Al fraction of the QWs is smaller. The maximum refractive index difference between the 100 Å GaAs/100 Å Al_0.2Ga_0.8As QWs at zero electric filed and bulk Al_0.1Ga_0.9As is about 0.044. Even with a small refractive index difference of 0.0132, the OFF-state reflectance of a normally-off MQW modulator at the designed photon wavelength will increase from the desired value of 0% to 90% when the reflectivity of the bottom mirror is 0.99     

GaAs和GaAs/AlGaAs多层量子阱中载流子的超快动力学(英文)

The ultrafast photoexcited carrier dynamics in bulk GaAs and GaAs/ AlGaAs multiple quantum well(MQW)structure has been studied using femtosecond laser pulse pump-probe techniques on the samples grown by MBE. A hot carrier cooling time of 1.5ps in MQW is measured at room temperature. Also, optical phonon emission at 33meV is observed in this sample. These results are found to be similar to that observed in bulk GaAs. A comparison of the hot carrier cooling rates for the two cases suggests that the infra-sub-band optical phonon scattering in MQW may play a dominant role in the cooling of highly excited hot carriers for the narrow wells. The experimental results agree well with that predicted by a simple infinite depth square-well model.     

High-performance Mach-Zehnder modulators in multiple quantum wellGaAs/AlGaAs

We demonstrate Mach-Zehnder interferometric waveguide intensity modulators which employ electrorefraction due to the quantum-confined Stark effect in multiple quantum well (MQW) GaAs/AlGaAs. These devices exhibit average half-wave voltage-length products as low as 3.0 V·mm and extinction ratios greater than 23.8 dB, which are superior to any MQW devices of this type. An effective index based model is developed to extract linear and quadratic electro-optic coefficients from the modulation data. Also, the power handling limitations of MQW modulators are discussed in terms of device performance and catastrophic electrical failure     

Metalorganic vapor phase epitaxy growth and properties of GaAs/AlGaAs and InGaAs/GaAs quantum well structures on (111)A GaAs substrates

We review the recent advances in the fabrication and properties of GaAs/AlGaAs and InGaAs/GaAs quantum well (QW) structures grown on (111)A GaAs substrates by atmospheric pressure metalorganic vapor phase epitaxy (MOVPE). We show that a 25-period GaAs/AlGaAs multi-QW (MQW) structure was fabricated with good crystal quality, high photoluminescence (PL) emission intensity and monolayer (ML) interfacial roughness. A PL full width at half maximum (FWHM) of 10.5 meV was achieved for a 25-period MQW with a well width of 44 Å. This is the narrowest linewidth reported to date for any similar structures grown on (111)A or B substrates by any growth technique. We also report the properties of an InGaAs/GaAs single quantum well structure grown on (111)A GaAs. For this structure, the PL FWHM value was 9.1 meV, corresponding to a 1 ML interfacial roughness for a well width of 41 Å. This is the first demonstration of an InGaAs/GaAs quantum well structure grown on (111)A or (111)B GaAs by MOVPE.     

Photoresponse study of normal incidence detection in p-type GaAs/AIGaAs multiple quantum wells

We studied p-type GaAs/AIGaAs multiple quantum well (MQW) materials as a possible alternative to the current n-type GaAs/AIGaAs MQWs for infrared detection. The advantage of p-type MQWs is that absorption of infrared radiation at normal incidence is not selection rule forbidden as it is for the n-type. We have verified that significant photoresponse occurs at normal incidence in p-type MQWs. We studied changes in the photoresponse spectrum as a function of well width and temperature. The MQW heterostructures were designed to use bound to continuum intersubband absorption in the GaAs valence band and to have a peak photoresponse near 8 μm. The photoresponse spectrum was compared to the first theoretical model of the bound to continuum absorption in p-type GaAs/ AlGaAs MQWs. The theoretical absorption curve was found to be in good qualitative agreement with the experimental results.     

Photoreflectance spectroscopy of low-dimensional GaAs/AlGaAs structures

Results of room-temperature photoreflectance measurements on three GaAs/Al_0.33Ga_0.67As multiquantum well (MQW) structures with three different widths of wells and on two GaAs/Al_0.33Ga_0.67As high-electron-mobility transistor (HEMT) structures are presented. Energy-gap-related transitions in GaAs and AlGaAs were observed. The Al content in AlGaAs was determined. MQW transition energies were determined using the first derivative of a Gaussian profile of the measured resonances. In order to identify the transitions in the MQS, the experimentally observed energies were compared with results of the envelope function calculation method for a rectangular quantum well. The Franz–Keldysh oscillation (FKO) model was also used to determine the built-in electric field in various parts of the investigated structures. The values of the electric fields allow us to hypothesise about the origin of these fields. © 1997 John Wiley & Sons, Ltd.     

AlGaAs/GaAs multiquantum-well (MQW) laser applied to monolithic integration with FET driver

A ridge-waveguide AlGaAs/GaAs multiquantum-well (MQW) laser has been monolithically integrated with two MESFETs on a semi-insulating GaAs substrate. The laser was grown in an etched groove to realise a nearly planar horizontal arrangement with FETs. This MQW laser was found to successfully achieve a CW operation with a lowthreshold current of 20 mA at room temperature.     

Anistropy and broadening of optical gain in a GaAs/AlGaAs multiquantum-well laser

Anisotropic property and spectral broadening of the optical gain in a GaAs/AlGaAs multi-quantum-well (MQW) laser were precisely measured and compared with theoretical calculation to acquire a profitable model for designing of MQW lasers. The anisotropic property was well explained with calculation of allowable orientation of the electron wave. The broadening of the gain spectrum was also well explained by taking into account effect of the intraband relaxation of the electron wave. The threshold current density in the MQW structure was theoretically estimated based on the model to be lower thanJ_{th} doteq 660A/cm².     

Nonlinear absorption in n-i-p-i-MQW structures

Absorptive nonlinearity in a GaAs/AlGaAs n-i-p-i-MQW (multiple quantum well) structure consisting of alternating n-AlGaAs, i-GaAs/AlGaAs MQW, and p-AlGaAs layers is investigated. A change in the absorption coefficient of more than 4000/cm is obtained in the i-MQW layer with an extremely low excitation intensity on the order of 1 mW/cm ². The figure of merit for absorptive nonlinearity, σ _ch, defined as the change in the absorption coefficient induced by excitation of an electron-hole pair per unit volume, is experimentally evaluated to be 7×10^-13 cm², which is an order of magnitude larger than that for saturation of excitonic absorption in a conventional MQW structure. This experimental value agrees well with the theoretical estimation, which is calculated assuming an optical nonlinear process     

Self-aligned index-guided multiple quantum well laser by sulphur diffusion-induced disordering

A simple self-aligned fabrication process for sulphur-diffusion disordered AlGaAs/GaAs multiple quantum well (MQW) lasers is described that produces refractive index guiding. However, the gradual profile of sulphur diffusion causes a separation between the disordered/nondisordered interface and the pn junction which leads to a large lateral optical loss of the index-guided mode.<>     

Study of the optical and structural properties of multi quantum well structures grown on high-index surfaces

The MOVPE overgrowth of high [0 1¯ 1]-oriented ridges confined at sides by facets related to {n 1 1} crystallographic planes is reported. We studied the influence of the side tilt on the thickness of the AlGaAs and GaAs epitaxial layers grown under the condition of the kinetic growth mode. The multi quantum well (MQW) structures were prepared on the sides of ridges tilted at 54.7°, 45° and 30° to (1 0 0). The sidewall surface morphologies before and after epitaxial growth were evaluated and compared. We observed no tendency towards planarization towards a neighbouring high-index crystallographic plane, such as (2 1 1) and (3 1 1). We also showed that the quantum wells of the MQW structure make a smooth transition over the edge between the top surface and the facet as both AlGaAs and GaAs grew at similar rates on the surfaces.     

MOCVD生长GaAs/AlGaAs量子阱研究

利用常压MOCVD技术在较低生长速率下生长出多种GaAs/AlGaAs多量子阱结构材料,利用低温PL谱和TEM对材料结构进行了表征。所得势阱和势垒结构厚度均匀平整,最窄阱宽为1.8nm。本研究表明,低速率(γ≤0.5nm/s)连续生长工艺能够避免杂质在界面富集,优于间断生长工艺,且在掺si n~+-GaAs衬底上所得量子阱发光强度高于掺Cr SI-GaAs衬底上的结果。     

Tradeoff between phase- and intensity modulation in GaAs/AlGaAsdouble heterostructure and multiple quantum well phase-modulatorwaveguides

The wavelength dependence of phase sensitivity (°/mm V) and intensity modulation of a double-heterostructure (DH) device and a multiquantum-well (MQW) device in the GaAs/AlGaAs material system is studied. The results show the tradeoff between phase modulation and intensity modulation and also show that, for the same intensity modulation, the MQW device produces twice as much phase modulation as the DH device. For example, at an intensity modulation of -1 dB the MQW device has a phase sensitivity of 120°/mm V while the DH device gives a value of ≈60°/mm V     

GaAs／Al_xGa_（1－x）As多量子阱红外探测器的光调制光谱研究

运用光调制光谱方法测量了ＧａＡｓ／ＡｌｘＧａ（１－ｘ）Ａｓ多量子阱红外探测器材料的调制反射谱，结果表明光调制光谱可以精确确定阱宽、Ａｌ组分、子带跃迁能量和探测峰值波长等许多重要参数，结合实验结果，采用Ｋｒｏｎｉｇ－Ｐｅｎｎｙ模型对材料能带结构进行了理论计算，与实验结果相符．