Effects of growth interruption on the optical properties of AIGaAs/GaAs and GaAs/InGaAs quantum wells grown by atmospheric pressure organometallic chemical vapor deposition

In this study, the effects of growth interruptions on Al_0.17Ga_0.83As/GaAs and GaAs/ In_xGa_1-xAs quantum wells (QWs) grown by organometallic chemical vapor deposition (OMCVD) were assessed using low-temperature photoluminescence (PL) and photoluminescence excitation (PLE) spectroscopies. Growth interruption times were varied between 60, 10, and 0 sec. For both material systems, as the interruption time was reduced, the ground-state QW transition energies increased, while the linewidths of the peaks decreased. For the Al_0.17Ga_0.83As/GaAs structures, 5 K PL data suggests that the incorporation of impurities is enhanced by longer growth interruption times. In addition, as the interruption time was reduced, the energy separation between the 5 K PL and PLE peaks (Stokes shift) decreased, and was as low as 2.6 meV for no interruption. For GaAs/In_0.11Ga_0.89As samples, 2 K PL data indicated that the incorporation of donor species was not a function of the growth interruption time.     

Photoluminescence characterization of the effects of rapid thermal annealing on AlGaAs/GaAs modulation-doped quantum wells

In this study, we describe the effects of rapid thermal annealing on the electrical and optical properties of modulation-doped quantum wells (MDQWs). The sheet carrier concentration in MDQW structures which have been annealed in contact with a piece of GaAs tends to decrease with increasing annealing time due to Si auto-compensation in the doped AlGaAs regions. The high energy cut-off point of 4.2 K PL spectra, which occurs at the Fermi energy, and the 77 K PL linewidth are accurate measures of sheet carrier density. These two parameters track variations in carrier density produced by annealing. Photoluminescence spectra also provide additional insight into annealing-induced changes such as Si migration, which causes a degradation in the mobility of the two-dimensional electron gas.     

Research on the photoluminescence of spectral broadening by rapid thermal annealing on InAs/GaAs quantum dots

Photoluminescence (PL) test was conducted to investigate the effect of rapid thermal annealing (RTA) on the optical performance of self-assembled InAs/GaAs quantum dots (QDs) at the temperatures of 16 and 300 K. It was found that after RTA treatment, the PL spectrum of the QDs sample had a large blue-shift and significantly broadened at 300 K. Compared with the as-grown InAs QDs sample, the PL spectral width has increased by 44.68 meV in the InAs QDs sample RTA-treated at 800 °C. The excitation power-dependent PL measurements showed that the broadening of the PL peaks of the RTA-treated InAs QDs should be related to the emission of the ground state (GS) of different-sized InAs QDs, the InAs wetting layer (WL) and the In_0.15Ga_0.85As strain reduction layer (SRL) in the epitaxial InAs/GaAs layers.     

Beryllium Ion Implantation into GaAs and Pseudomorphic AIGaAs/lnGaAs/GaAs Heterostructure

Implantations of Be, Be + P, Be + F, Be + P +F, BeF and Mg + P into GaAs and AlGaAs/InGaAs/GaAs pseudomorphic heterostructure were evaluated by secondary ion mass spectrometry profilings and electrical resistivity measurements. Rapid thermal annealing causes a strong diffusion of Be when implanted alone. Co-implantation with P prevents both diffusion and degradation of the Gaussian-shape implant distribution and thus improves the semiconductor sheet resistivity. Annealing at 850°C for 10 s for a Be + P co-implant results in a 60% activation efficiency, and lower diffusion and resistivity when compared to single Be, Be + F, Be + F + P, BeF, and Mg + P implanted at the same dose.     

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.     

GaAs／AlGaAs窄量子阱中激子二维特性的退化

用光荧光（ＰＬ）和时间分辨光谱（ＴＲＰＬ）技术研究了ＧａＡＳ／ＡＩＧａＡＳ量子阱结构中荧光上升时间τｆ和激子谱线半宽（ＦＷＨＭ）随阱宽的变化关系，发现在窄阱中，τｆ，随阱宽的变化关系与宽阱时的情况恰恰相反，在窄阱中τｆ随着阱宽的减小而增加，归结为激子二维特性的退化导致声学声子对激子的散射作用减弱造成的．同时观测到窄阱中谱线半宽随着阱宽减小而增加，这也是因为激子特性由维二维向三维转化造成的．     

Hot exciton effects and relaxation in coupled quantum wells

By studying photoluminescence and photoluminescence excitation in coupled quantum wells, we have studied the influence of the tunneling time on the relaxation of the photoexcited carriers. The ability to vary the coupling strength by the barrier thickness, allowed us to evidence hot exciton relaxation effects as well as resonant Raman scattering.     

Intervalley scattering in GaAs/AlGaAs quantum wells and quantum cascade lasers

The results of simulations of Γ−X scattering in GaAs/AlGaAs quantum wells are presented, discussing the importance of the mole fraction, doping density, and lattice and electron temperatures in determining the scattering rates. A systematic study of Γ−X scattering in GaAs/Al_xGa_1−xAs heterostructures, using a single quantum well to determine the importance of well width, molar concentration x, lattice temperature, and doping density, has been performed. After this we consider a double quantum well to determine the role of intervalley scattering in the transport through single-layer heterostructures, i.e. Γ−X−Γ scattering compared with Γ−Γ scattering. Finally, we estimate the relative importance of intervalley scattering in a GaAs-based quantum-cascade laser device and compare it with other relevant scattering mechanisms important to describe carrier dynamics in the structure. Our simulations suggest that Γ−X scattering can be significant at room temperature but falls off rapidly at lower temperatures.     

Two electron transitions of the exciton bound at the Si Donor confined in GaAs/AlxGa1-xAs quantum wells

The exciton bound to the shallow Si-donor confined in a 100A wide GaAs quantum well has been studied in selective photoluminescence (SPL) and photoluminescence excitation (PLE) spectroscopy. The transition from the ground state, ls(Γ₆), to the first excited state, 2s(Γ₆), of the confined Si donor has been observed via two-electron transitions (TETs) of the donor bound exciton observed in SPL for the first time to the best of our knowledge. The interpretation of the TET peaks is confirmed by PLE measurements. Further, from Zeeman measurements, the magnetic field dependence of the donor ls(Γ₆)-2s(Γ₆) transition energy has been determined.     

Effects of Rapid Thermal Annealing on Optical Properties of GaInNAs/GaAs Single Quantum Well Grown by Plasma-Assisted Molecular Beam Epitaxy

The effects of Rapid Thermal Annealing (RTA) on the optical properties of GaInNAs/GaAs Single Quantum Well (SQW) grown by plasma-assisted molecular beam epitaxy are investigated. Ion removal magnets were applied to reduce the ion damage during the growth process and the optical properties of GaInNAs/GaAs SQW are remarkably improved.RTA was carried out at 650℃ and its effect was studied by the comparising the roomtemperature PhotoLuminescence (PL) spectra for the non ion-removed (grown without magnets) sample with for the ion-removed (grown with magnets) one. The more significant improvement of PL characteristics for non ion-removed GaInNAs/GaAs SQW after annealing (compared with those for ion-removed) indicates that the nonradiative centers removed by RTA at 650℃ are mainly originated from ion damage. After annealing the PL blue shift for non ionremoved GaInNAs/GaAs SQW is much larger than those for InGaAs/GaAs and ion-removed GaInNAs/GaAs SQW. It is found that the larger PL blue shift of GaInNAs/GaAs SQW is due to the defect-assisted In-Ga interdiffusion rather than defect-assisted N-As interdiffusion.     

Effects of Rapid Thermal Annealing on Optical Properties of GaInNAs/GaAs Single Quantum Well Grown by Plasma-Assisted Molecular Beam Epitaxy

The effects of Rapid Thermal Annealing (RTA) on the optical properties of GaInNAs/GaAs Single Quantum Well (SQW) grown by plasma assisted molecular beam epitaxy are investigated. Ion removal magnets were applied to reduce the ion damage during the growth process and the optical properties of GaInNAs/GaAs SQW are remarkably improved. RTA was carried out at 650℃ and its effect was studied by the comparising the room\|temperature PhotoLuminescence (PL) spectra for the non ion removed (grown without magnets) sample with for the ion removed (grown with magnets) one. The more significant improvement of PL characteristics for non ion removed GaInNAs/GaAs SQW after annealing (compared with those for ion removed) indicates that the nonradiative centers removed by RTA at 650℃ are mainly originated from ion damage. After annealing the PL blue shift for non ion removed GaInNAs/GaAs SQW is much larger than those for InGaAs/GaAs and ion removed GaInNAs/GaAs SQW. It is found that the larger PL blue shift of GaInNAs/GaAs SQW is due to the defect assisted In Ga interdiffusion rather than defect assisted N As interdiffusion.     

Growth and optical characterization of strained CdZnTe/ CdTe quantum wells

We have grown strained Cd_1-xZn_xTe(x ≈ 0.2)/CdTe single and multiple quantum wells by molecular beam epitaxy. GaAs was used as a substrate. The well widths were systematically increased until the critical thickness was exceeded. Low-temperature (liquid helium) photoluminescence (PL) spectroscopy was used to characterize the films. Two prominent PL peaks were observed: one arising from the quantum well and the other from the barrier material. The energy of the quantum well luminescence is consistent with theory when strain is included. The critical layer thickness for the CdTe quantum wells was found to be between 150 and 175 å, in agreement with the model of Matthews and Blakeslee.     

Photoluminescence characteristics of GaN/lnGaN/GaN quantum wells

Photoluminescence (PL) characteristics of GaN/lnGaN/GaN single quantum wells (QWs) and an InGaN/GaN single heterojunction were studied using continuous wave (CW) and pulsed photoluminescence in both edge and surface emitting configurations. Samples were grown on c-plane sapphire substrates by atmospheric pressure metalorganic chemical vapor deposition (MOCVD). Room temperature and 77K PL measurements were performed using a CW Ar-ion laser (305 nm) and a frequency tripled (280 nm), pulsed, mode-locked Ti: sapphire laser. CW PL emission spectra from the quantum wells (24, 30, 80Å) were all blue shifted with respect to the reference sample. The difference (i. e., the blue shift) between the measured value of peak emission energy from the QW and the band-edge emission from the reference sample was attributed to quantum size effects, and to strain arising due to a significant lattice mismatch between InGaN and GaN. In addition, stimulated emission was observed from an InGaN/GaN single heterojunction in the edge and surface emitting configu-ration at 77K. The narrowing of emission spectra, the nonlinear dependence of output emission intensity on input power density, and the observation of a strongly polarized output are presented.     

Single-mode GaAs/AIGaAs quantum cascade microlasers

Single-mode edge emitting GaAs/AlGaAs quantum cascade microlasers at a wavelength of about 11.4μm were realized by shortening the Fabry-Perot cavity length. The spacing of the longitudinal resonator modes is inversely proportional to the cavity length. Stable single-mode emission with a side mode suppression ratio of about 19 dB at 85 K for a 150-μm-long device was demonstrated.     

Contactless electroreflectance of GaInN/AlInN multi quantum wells: The issue of broadening of optical transitions

Contactless electroreflectance (CER) has been applied to investigate the energy and broadening of the fundamental transition for GaInN/AlInN multi quantum wells (MQWs) with the width varies from 1.3 to 1.8 nm. It has been found that the broadening of GaInN bulk-like transition equals ∼280 meV and increases significantly going to GaInN quantum wells (QWs). In order to explain experimental data, a simple theoretical analysis has been performed. It has been shown that the observed variation of broadening for the fundamental transition is associated with the QW width fluctuations. In addition, it has been estimated that the maximal width fluctuations in these MQWs equal ∼2 ML (∼30% of the QW width). Such a significant QW width fluctuations are attributed to the incorporation of indium atoms into this material system.     

Pulsed laser annealing of self-organized InAs/GaAs quantum dots

The effect of pulsed laser annealing (PLA), using an excimer laser, on the luminescence efficiency of self-organized InAs/GaAs and In_0.4Ga_0.6As/GaAs quantum dots has been investigated. It is found that such annealing can enhance both the peak and integrated photoluminescence (PL) efficiency of the dots, up to a factor of 5–10 compared to as-grown samples, without any spectral shift of the luminescence spectrum. The improved luminescence is attributed to the annealing of nonradiative point and extended defects in and around the dots.     

Uniform intermixing of quantum wells in p-i-n modulator structures by impurity free vacancy diffusion

We present the results of an investigation of impurity free vacancy diffusion (IFVD) post-growth treatments of p-i-n modulator structures. The investigation is in two parts. We first establish that gallium vacancies (V_Ga) are produced during IFVD (by measuring the intensity of the low temperature 1.2 eV signal from Si-V_Ga complexes) in a thick Si-doped GaAs sample. The second part of this work investigates the degree of intermixing of three 80Å GaAs quantum wells embedded in the intrinsic region of a p-i-n modulator at depths between 1–2 μm from the surface. Photoluminescence studies on etched samples and cathodoluminescence showed that no significant depth dependence occurs as a result of IFVD.     

Photoluminescence excitation spectroscopy of InAs0.67P0.33/InP strained single quantum wells

The optical emission characteristics of biaxially compressed InAs _x P_{1− x} /InP strained single quantum well (QW) structures, with nominal compositionx=0.67, have been investigated using photoluminescence (PL) and photoluminescence excitation (PLE) spectroscopies. The highly strained QWs exhibit intense and narrow PL in the 0.9–1.5 μm wavelength range, similar to the lattice-matched InGaAs(P)/InP system. The 20 K PLE spectra exhibit well-resolved features attributed ton=1 heavy hole (E1H1) and light hole (E1L1) transitions in the 1.0–1.5 μm wavelength range. In addition, features attributed to transitions betweenn=2 electrons and heavy holes (E2H2), and betweenn=1 electrons and unconfined holes (E1Hf), were observed. The energy splitting between the heavy-hole and light-hole bands was found to be a sensitive measure of the band offsets in the system. The best prediction of this splitting was obtained for a valence band offset of δE _V ∼0.25δE _G . This value of band offset was in agreement with the energy position of the E1Hf transition. The observed transition energies were also compared with the results of a finite square well model, taking into account the effects of strain, and the results offer further support for the band offset assignment. This study indicates that the InAsP system may be advantageous for application in strained-layer optoelectronic devices operating in the 1.3–1.6 μm wavelength range.     

Hot-electron magnetophonon resonances in doped and undoped GaAs/(Ga,Al)As quantum wells studied using photoluminescence

Hot-electron magnetophonon resonances in the effective temperature T_eff of photo-excited carriers in GaAs/Al_xGa_1-xAs quantum wells have been observed using photoluminescence for the first time. The technique has been demonstrated to be applicable to both doped and undoped structures, allowing the hot-electron magnetophonon effect in the latter to be studied. The experimental data are in good agreement with values of T_eff=T_eff(B) calculated using a modell or the energy relaxation of hot two-dimensional carriers in a strong magnetic field.     

Si掺杂的AlGaInP/GaInP多量子阱光学特性

低压MOCVD方法生长了掺Si与不掺Si的AlGaInP/GaInP多量子阱结构,运用X射线双晶衍射与光荧光技术研究了掺Si对量子阱性能的影响.测试结果表明掺Si使量子阱的生长速度增加,掺Si量子阱的光荧光强度比未掺Si量子阱的光荧光强度改善了一个数量级.