A study of impurity-free vacancy disordering in GaAs-AlGaAs forimproved modeling

A study of the parameters of the process of impurity-free vacancy disordering (IFVD) of GaAs-AlGaAs quantum-well structures is presented. The study includes photoluminescence excitation measurements which show that the as-grown barrier/well interface is better fitted by an exponential profile than a square profile. This has a significant effect on the intermixed diffusion profiles. Also, deep level transient spectroscopy measurements have been conducted on samples that were processed using IFVD. The measurements show an elevated concentration of the trap EL2 in the processed samples, which is known to be related to As antisites. The concentration of such defects agrees with the concentration calculated for IFVD to within an order of magnitude, suggesting a correlation between the point defects required for IFVD and EL2. Finally, temporally and spatially resolved photoluminescence measurements were conducted on processed samples which indicate a factor of 3 reduction in the photogenerated carrier life time after undergoing IFVD. A spatial resolution better than 3 μm has been observed     

CW and mode-locked integrated extended cavity lasers fabricatedusing impurity free vacancy disordering

A phosphorus-doped silica (P:SiO₂) cap containing 5 wt% P has been demonstrated to inhibit the bandgap shifts of p-i-n and n-i-p GaAs-AlGaAs quantum-well laser structures during rapid thermal processing. Bandgap shift differences as large as 100 meV have been observed between samples capped with SiO₂ and with P:SiO₂. The technique has been used to fabricate GaAs-AlGaAs ridge lasers with integrated transparent waveguides. With a selective differential blue-shift of 30 nm in the absorption edge, devices with 400 μm/2.73-mm-long active/passive sections exhibited an average threshold current of 9 mA in continuous-wave (CW) operation, only 2.2 mA higher than that of discrete lasers of the same active length and from the same chip. Extended cavity mode-locked lasers were also investigated and compared to all active devices. For the extended cavity device, the threshold current is a factor of 3-5 lower, the pulsewidth is reduced from 10.3 to 3.5 ps and there is a decrease in the free-running jitter level from 15 ps (measurement bandwidth 10 kHz-10 MHz) to 6 ps. In addition, the extended cavity lasers do not exhibit any self-pulsing modulation of the mode-locked pulse train, unlike the all-active lasers, and the optical spectra indicate that the pulses are more linearly chirped     

Dependence of dielectric-cap quantum-well disordering ofGaAs-AlGaAs quantum-well structure on the hydrogen content in SiNx capping layer

Dielectric-cap quantum-well disordering of GaAs-AlGaAs multiple-quantum-well (MQW) structure was carried out using SiN_x capping layer grown by plasma enhanced chemical vapor deposition. There was a dependence of quantum-well disordering (QWD) on the hydrogen content in the SiN_x capping layer, which was varied by changing the NH₃ flow rate during the film growth. The degree of QWD increased with increasing of hydrogen content in the Si_x capping layer. The degree of QWD with SIN, capping layer grown at higher NH₃ flow rate was comparable to that with a 300-nm-thick SiO₂ capping layer at the same rapid thermal annealing condition. This result implies the possibility of obtaining spatially selective disordered MQW structure using SiN_x capping layers grown at different NH₃ flow rates. The effect of different SiN_x capping layers on QWD was characterized semiquantitatively by introducing relative vacancy density     

GaAs-based modulation-doped quantum-well infrared photodetectors for single- and two-color detection in 3-5 /spl mu/m

Double-barrier quantum-well infrared photodetectors are promising for operation in the midinfrared region. In this paper, we present a series of novel molecular beam epitaxy (MBE)-grown devices based on modulation-doped (MD) AlGaAs-AlAs-GaAs structures that exhibit a remarkable responsivity at zero bias (0.05 A/W) at 4.6 /spl mu/m. Since the photovoltaic properties are strongly dependent on the symmetry of the potential profile, we have systematically varied the position of the dopant in the barriers for a series of single-color detectors. Low-temperature photocurrent spectra and current-voltage (I-V) characteristics (in the dark and under illumination) show that the location of the dopant is a relevant design parameter, due to its role in the photovoltaic behavior (i.e., the presence or absence of zero bias signal). The performance of the MD devices is compared with that of a detector with doping in the center of the well and otherwise the same structure. In particular, the responsivity and detectivity seem to be higher for the MD detectors than for well-doped samples, especially when the dopant is located in the barrier closest to the substrate. Therefore, we have chosen that MD dopant profile when designing and growing, to our knowledge, the first 3-5 /spl mu/m two-color detector, with simultaneous detection at 3.8 and 4.4 /spl mu/m.     

Impurity-induced layer disordering of quantum-wellheterostructures: discovery and prospects

The circumstances leading to the discovery in 1980 of impurity-induced layer disordering (IILD) of AlAs-GaAs (Al_xGa _1-xAs) quantum-well heterostructures (QWHs) and superlattices (SLs) are described. In view of the great stability of a QWH or SL (AlAs-GaAs) against ordinary thermal annealing, IILD came as a surprise, i.e., the lower temperature (selective) change from red-gap QW crystal to yellow-gap bulk crystal. Layer disordering can be carried out most effectively, via diffusion or implantation, with two-site dopants such as Zn (acceptor) or Si (donor), but is not restricted to active impurities alone. This maskable planar technology, which (with crystal conservation) transforms a coarser layered III-V “alloy” to a smoother stochastic alloy, and higher bandgap, is capable of forming, as desired, regions that confine carriers and photons. Accordingly, IILD has broad and growing use in optoelectronics (lasers, waveguides, etc.), particularly for III-V systems employing Al and Ga which easily substitute for one another and are sensitive to IILD. The atomic rearrangement of diffusion, a small scale (microscopic) lattice change, is in essence “amplified” by IILD into a large scale (macroscopic) layer change (patterned) that provides a method to study III-V diffusion mechanisms. IILD, a planar technology and growing area of work, is useful in optoelectronics applications as well as for basic diffusion studies in III-Vs and potentially other crystal systems     

Theoretical analysis of diffused quantum-well lasers and optical amplifiers

Diffused quantum-well (QW) distributed feedback (DFB) lasers and optical amplifiers will be theoretically analyzed in this paper. For DFB lasers, a design rule will be proposed and the validity of the design rule will be discussed with respect to changes in the injected carrier density. The range of grating period, which can be used in the design, is discussed. As a consequence, the maximum tuning range of the emission wavelength can be estimated without involving the time-consuming self-consistent simulation. The features of polarization independence of optical amplifiers achieved by using diffused QWs are also discussed. Our theoretical results successfully explain why polarization independence can achieve in the long-wavelength tail of the modal gain and absorption coefficient but not at photon energies above the transition edge. This explanation applies to other tensile-strained QWs for polarization-independent applications. The understanding is crucial for optimizing polarization-independent devices. To conclude, our analysis of the diffused QW optical devices demonstrates that QW intermixing technology is a practical candidate for not only realizing monolithic photonic integrated circuit, but also enhancing optical device performance.     

Comprehensive modeling of diffused quantum-well vertical-cavitysurface-emitting lasers

A numerical model for investigating the thermal, electrical, and optical characteristics of vertical-cavity surface-emitting: lasers (VCSELs) with a diffused quantum-well (QW) structure is presented. In the model, the quasi-three-dimensional (quasi-3-D) distribution of temperature, voltage and optical fields as well as the quasi-two-dimensional (quasi-2-D) diffusion and recombination of carrier concentration inside the QW active layer are calculated in a self-consistent manner. In addition, the quasi-3-D distribution of implanted ions before and after thermal annealing are computed. The variation of electrical conductivity and absorption loss as well as the influence of impurity induced compositional disordering on the optical gain and refractive index of the QW active layer are also taken into consideration. Using this model, the steady-state characteristics of diffused QW VCSELs are studied theoretically. It is shown that significant improvement of stable single-mode operation can be obtained using diffused QW structure     

Interdiffusion induced modification of surface-acoustic-waveAlGaAs-GaAs quantum-well modulators

A theoretical study of short period AlGaAs-GaAs diffused quantum-well (QW) absorption modulators operated by using surface acoustic waves (SAWs) is carried out in this paper. The as-grown QW structure is optimized and interdiffusion is used to fine tune the modulation performance. The results show that a stack of QWs can be developed at the top surface of the modulator to utilize the steep potential induced by SAWs. The optimized structure can also produce a large absorption change and thus a fast modulation speed for the same modulation depth. In comparison to previous results, the required surface acoustic wave has a longer wavelength and a lower power so that the fabrication of the interdigital transducer can be simplified. In addition, the use of interdiffusion can provide an useful fine adjustment to the operating wavelength, further enhancement of the modulation depth and an improvement in chirping with the only drawback of an increased absorption loss     

Design of a SiGe-Si quantum-well optical modulator

A light modulator consisting of modulation-doped SiGe-Si multiple quantum wells integrated in a silicon-on-insulator waveguide is designed. The device is based on the electrorefractive effect due to the variation of holes density in the SiGe wells, induced by applying a reverse bias on a PIN diode. This mechanism is simulated by numerical calculations of the hole distribution coupled with the optical guided mode propagation characteristics. The mode effective index variation of TE-polarized light at the 1.31-/spl mu/m wavelength can then be obtained as a function of the applied bias. The influences of the structure parameters such as the thickness and the doping level of the doped barrier layers or the number of SiGe wells is analyzed thanks to a design of experiment method. The optimization gives an effective index variation of 2.10/sup -4/ for an applied bias voltage of 6 V. To obtain optical intensity modulation, this structure has to be included in a Fabry-Perot cavity. The modulation performances are analyzed.     

Large- and small-signal dynamic behavior of high-speeddual-polarization quantum-well semiconductor lasers

The transmission-line laser model is modified to model both transverse-electric (TE) and transverse-magnetic (TM) modes so that it is applicable to quantum-well (QW) dual-polarization lasers and polarization-insensitive semiconductor optical amplifiers (SOAs). The effects of carrier transport are also included in the model. The resulting dual-polarization transmission-line laser model is used to study large- and small-signal dynamic behavior of dual-polarization lasers. We find from large-signal simulations that the polarization asymmetry (ratio of the transverse-modal powers) varies on a nanosecond time scale in dual-polarization single-quantum-well (SQW) devices. We show that unequal transverse-modal differential gains and gain nonlinearities are responsible for this temporal polarization asymmetry. In addition, our numerical simulations show that the steady-state polarization asymmetry is a strong function of the gain nonlinearity. Small-signal dynamic simulations show that the modulation response of the polarization-unresolved output of dual-polarization SQW lasers follows that of the transverse mode with the lowest gain nonlinearity coefficient, regardless of the transverse-modal differential gains     

Modeling of carrier dynamics in quantum-well electroabsorption modulators

We present a comprehensive drift-diffusion-type electroabsorption modulator (EAM) model. The model allows us to investigate both steady-state properties and to follow the sweep-out of carriers after pulsed optical excitation. Furthermore, it allows for the investigation of the influence that various design parameters have on the device properties, in particular how they affect the carrier dynamics and the corresponding field dynamics. A number of different types of results are presented. We calculate absorption spectra and steady-state field screening due to carrier pile-up at the separate-confinement heterobarriers. We then move on to look at carrier sweep-out upon short-pulse optical excitation. For a structure with one well, we analyze how the well position affects the carrier sweep-out and the absorption recovery. We calculate the field dynamics in a multiquantum-well structure and discuss how the changes in the field near each well affect the escape of carriers from that well. Finally, we look at the influence that the separate-confinement heterostructure barriers have on the carrier sweep-out.     

Area selectivity of InGaAsP-InP multiquantum-well intermixing byimpurity-free vacancy diffusion

Area selectivity of bandgap tuning in the InGaAsP-InP multiquantum-well structure has been investigated using low temperature photoluminescence (PL). The bandgap blue-shift in the intermixed region was as much as 170 meV for a rapid thermal anneal of 30 s at 850°C, and was controllable using annealing temperature and time. From samples with SiO₂ stripe patterns, clearly separated PL peaks were observed centered at 0.95 and 1.08 eV, each representing signals originating from the dielectric capped and exposed areas, respectively. In samples with stripes intervals less than 6 μm, PL signals did not separate, but formed one broad spectrum due to lateral diffusion. The lateral diffusion was found less than 3.0 μm     

Orientation dependence of optical properties in long wavelengthstrained quantum-well lasers

The dependence of optical properties on crystal orientation is analyzed for long wavelength strained quantum-well (QW) GaAsP-InGaAsP lasers. The calculation is based on the multiband effective mass theory which enables us to consider the anisotropy and the nonparabolicity of the valence-band dispersions. It is found that the optical gain increases as the crystal orientation is inclined from (001) toward (110). This is due to the reduced valence-band density of states. The differential gain is about 1.6 times larger for the (110)-oriented 1.55-μm strained QW's than for equivalent (001)-oriented QW's. It is also shown that the threshold current density in 1.3-μm strained QW lasers decreases to two-thirds of that in the (001)-oriented laser as the orientation is inclined away from (001) by 40°-90     

Photoluminescence, Raman, and infrared diagnosis of GaAs-AlGaAssuperlattices for intersubband infrared detection

We present optical diagnosis of GaAs-AlGaAs superlattices grown by molecular beam epitaxy for use as 8-20 μm infrared detectors, that combines photoluminescence, Raman, and Fourier transform infrared spectroscopies. Various structural and physical parameters were obtained by theoretical analysis of the optical results. The use of multiple optical techniques offers comprehensive characterization and further understanding of the physics of long wavelength infrared detectors     

Modification of modal gain in InGaAs-GaAs quantum-well lasers dueto barrier-state carriers

This paper describes the effects of barrier-state carriers on the modal gain of InGaAs-GaAs quantum-well (QW) lasers emitting at 980 nm. Experimental studies and numerical simulations are used to examine several drive configurations, each having a unique effect on the laser response. These include compound drive current shapes, optical excitations and fast electrical drives with rise times shorter than 100 ps. We demonstrate that a large barrier-state carrier density affects the index of refraction sufficiently so as to cause a reduction in the confinement factor and modal gain which is large enough to turn the laser off     

Wafer level reliability and lifetime analysis of InGaAsP/InP quantum-well Fabry-Perot laser diode

This paper investigated the reliability of semiconductor 1.3-/spl mu/m multiquantum-well (MQW) Fabry-Perot laser diodes (LDs) in a quarter 2-in wafer level that are measured to have uniform threshold currents, slope efficiencies, and wavelengths within 4% of the maximum deviation. By performing the accelerated aging test under a constant optical power of 3 mW at 85/spl deg/C for 2100 h, the lifetime of the fabricated optoelectronic devices was estimated, where the failure rate was matched on the fitted line of the lognormal distribution model resulting in the mean-time-to-failure (MTTF) of 2/spl times/10/sup 6/ h operating at room temperature.     

Fabrication of infrared photodetectors

Abstract

This paper presents the fabrication of an integrated optoelectronic circuit consisting of a waveguide and photodetector. Fabrication of the waveguides took place in a RIBE system with 1·5 sccm CH₄/H₂ (60:40) and 0·5 sccm Ar. Wet etching defines the photodetector regions. The detection of surface damage is minimal, using a novel differential optical reflectance technique.     

红外测温仪的设计

为了克服传统的温度计测量温度的主要缺点--需要测量者与被测目标近距离接触和测量不方便.在顾及仪器测量高精度前提下,以追求最低成本为原则,本文设计了红外测温仪的整体系统构架.接着根据热释电原理,主要针对人体体温测量进行了具体的设计开发,开发包括硬件电路,外围工艺,单片机程序和主机程序.并利用设计出来的红外测温仪在环境温度30 ℃下对人体温度和水温进行了测量,对人体的温度测量的误差低于±0.1 ℃.     

一种使用红外线和超声波的定位技术

本文提出了一种使用红外线和超声波的定位技术,对其工作原理和主要部分的实现方法进行了介绍,设计了测量脉冲调理电路接收超声信号,并分析了主要的误差源。该技术使用红外编码指令触发定位,扩大了定位范围,降低了功耗;在接收电路中加入共振电路,减小了外界干扰。通过大量实验,分析了环境温度、传播角度等因素对测距精度的影响。     

High-performance 1200-nm InGaAs and 1300-nm InGaAsN quantum-well lasers by metalorganic chemical vapor deposition

In this paper, we present the characteristics of high-performance strain-compensated MOCVD-grown 1200-nm InGaAs and 1300-nm InGaAsN quantum-well (QW) lasers using AsH/sub 3/ and U-Dimethylhydrazine as the group V precursors. The design of the InGaAsN QW active region utilizes an In-content of approximately 40%, which requires only approximately 0.5% N-content to realize emission wavelengths up to 1315-nm. Threshold current densities of only 65-90 A/cm/sup 2/ were realized for InGaAs QW lasers, with emission wavelength of 1170-1233 nm. Room-temperature threshold and transparency current densities of 210 and 75-80 A/cm/sup 2/, respectively, have been realized for InGaAsN QW lasers with emission wavelength of 1300-nm. Despite the utilization of the highly-strained InGaAsN QW, double-QW lasers have been realized with excellent lasing performance.