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.     

Critical thickness of GaAs/InGaAs and AlGaAs/GaAsP strained quantum wells grown by organometallic chemical vapor deposition

In this paper we describe a study of strained quantum wells (QWs) as a means to experimentally observe the critical thickness (h _c) for the formation of interfacial misfit dislocations. Two material systems were investigated: GaAs/In_0.11Ga_0.89As, in which the QW layers are under biaxialcompression, and Al_0.35Ga_0.65As/GaAs_0.82P_0.18, in which the QW layers are under biaxialtension. Samples were grown by atmospheric pressure organometallic chemical vapor deposition, and characterized by low-temperature photoluminescence (PL), x-ray diffraction, optical microscopy, and Hall measurements. For both material systems, the observed onset of dislocation formation agrees well with the force-balance model assuming a double-kink mechanism. However, overall results indicate that the relaxation is inhomogeneous. Annealing at 800–850° C had no significant effect on the PL spectra, signifying that even layers that have exceededh _c and have undergone partial relaxation are thermodynamically stable against further dislocation propagation.     

Photoluminescence and interface abruptness in InGaAsP/InGaAsP quantum wells

Quantum well (QW) structures consisting of InGaAsP wells and InGaAsP barriers grown by gas-source molecular beam epitaxy have been examined by low temperature photoluminescence (PL) in order to evaluate the contributions of compositional fluctuations in the quaternary alloy and of interface roughness to the PL linewidth. The well material was InGaAsP with a bandgap corresponding to a wavelength of 1.3 μm and the barrier material was InGaAsP of 1.15 μm. The theory for QW excitonic linewidths as a function of well thickness L_z due to fluctuations in alloy composition has been extended to include the case of the quaternary InGaAsP barrier. If the interfaces are atomically abrupt, the linewidth is dominated by compositional fluctuations in the well at large L_z and compositional fluctuations in the barrier at small L_z. The theory predicts a weak dependence of the linewidth on L_z since the composition of the well and barrier are similar. For rough heterointerfaces, the theory indicates the usual increase in linewidth with decreasing L_z. Photoluminescence measurements at 13K in arrays of single InGaAsP/InGaAsP QWs with L_z from 1.0 to 6.0 nm show only a weak variation of the full width at half maximum (FWHM) with L_z, in agreement with the theory for smooth interfaces. Furthermore, the lowest measured FWHM of 8.9 meV was found for a narrow well of L_z=1.8 nm, indicating the InGaAsP/InGaAsP interfaces are smooth and that the PL linewidth is dominated by compositional fluctuations.     

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.     

Low-Temperature photoluminescence of SiGe/Si disordered multiple quantum wells and quantum well wires

Low-temperature photoluminescence from disordered SiGe/Si quantum wells and quantum wires made from periodic quantum wells by electron beam lithography and reactive ion etching has been measured. No enhancement in luminescence is seen, compared to that in periodic quantum wells, in the disordered wells or quantum wires. New transitions are observed in the wire luminescence, including a possible no-phonon transition exhibiting a 32 meV blue shift compared to the same transition in the wells.     

Photoluminescence of InAs quantum dots coupled to a two-dimensional electron gas

Self-assembled InAs quantum dots have been extensively studied by a variety of experimental techniques. Works have been done on the transport properties of the InAs dots located near a two-dimensional electron gas (2DEG). However, there have been few reports on the optical properties of the InAs dots located closely to 2DEG. In this work, InAs dots samples with 2DEG and without 2DEG growth by solid source molecular beam epitaxy were studied using photoluminescence measurements. Different photoluminescence behaviors between the InAs dots and the InAs dots near the 2DEG were observed. It was found that the emission efficiency of the InAs dots was significantly enhanced by the existence of the nearby 2DEG and the thermal activation energy of the InAs dots was decreased by the 2DEG. It was speculated that the 2DEG at the AlGaAs/GaAs interface worked as an electron reservoir to the InAs dots. As a result, the conduction band between the dots and 2DEG is lowered, and thus the thermal activation energy of PL is lowered. It was concluded that in this way the optical properties of the InAs quantum dots could be tailored for optical applications.     

Optimal growth interrupts for very high quality InGaAs(P)/InP superlattices grown by MOVPE

The effects of different growth interrupt schemes at the compositional interfaces in 30 period InGaAs(P)/InP superlattices grown by metal-organic vapor phase epitaxy have been studied for quarternary compositions λ = 1.35 and 1.52 μm as well as for the ternary case λ = 1.67 μm. The best full width at half maximum of the photoluminescence peaks at 4 K are 7–8 meV for the InGaAsP/InP and 4.6 meV for the InGaAs/InP superlattices indicating extremely high optical quality and vertical homogenity of the samples. However, strong memory effects relating to both the presence and the absence of arsenic are evident from x-ray diffraction measurements. Reactor purging as a remedy is limited by the surface roughening and defect formation induced by a non-equilibrium vapor phase composition. Optimal growth interrupts must therefore be determined considering both the interface smoothness and abruptness and will in general be composition dependent.     

Optical investigations of strained InGaAs quantum wells

InGaAs/GaAs MOCVD-grown quantum wells have been investigated. Photoluminescence (PL) measurements have shown heavy-hole-related excitonic transitions within the temperature range from 10 to 100 K for all samples. In room-temperature photoreflectance (PR), sharp heavy- and light-hole excitonic transitions in the quantum wells have been observed. The transition energies obtained have been compared with values derived from theoretical considerations using the envelope function model including lattice-mismatch-related stress. The heavy- and light-hole transitions have been identified as excitonic transitions of types I and II respectively. © 1997 John Wiley & Sons, Ltd.     

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.     

快速热退火提高应变InAs／InP量子阱结构的晶体质量

研究了快速热退火对应变ＩｎＡｓ／ＩｎＰ单晶子阱结构光学性质的影响。样品经最佳条件７００℃，５ｓ的快速热退火，８Ｋ温度下量子阱的荧光强度地加了４倍，量子阱荧光峰仅蓝移１．５ｍｅＶ。     

Temperature dependent optical properties of self-organized InAs/GaAs quantum dots

We report photoluminescence (PL), time-resolved PL, and PL excitation experiments on InAs/GaAs quantum dots (QDs) of different size as a function of temperature. The results indicate that both the inhomogeneous properties of the ensemble and the intrinsic properties of single QDs are important in understanding the temperature-dependence of the optical properties. With increasing temperature, excitons are shown to assume a local equilibrium distribution between the localized QD states, whereas the formation of a position-independent Fermi-level is prevented by carrier-loss to the barrier dominating thermally stimulated lateral carrier transfer. The carrier capture rate is found to decrease with increasing temperature and, at room temperature, long escape-limited ground state lifetimes of some 10 ps are estimated. PL spectra excited resonantly in the ground state transition show matching ground state absorption and emission, indicating the intrinsic nature of exciton recombination in the QDs. Finally, the PL excitation spectra are shown to reveal size-selectively the QD absorption, demonstrating the quantum-size effect of the excited state splitting.     

Photoluminescence and electroreflectance studies of modulation-doped pseudomorphic AlGaAs/InGaAs/GaAs quantum wells

In this study, we describe the correlations between the photoluminescence (PL) spectra and electrical properties of pseudomorphic modulation-doped AlGaAs/InGaAs/GaAs quantum wells (MDQWs) grown by molecular beam epitaxy. In MDQWs, the presence of a large sheet carrier density contributes significantly to the PL linewidth. At low temperatures (4.2 K), free carrier induced broadening of the PL linewidth is influenced by the material quality of the structure. At higher temperatures (77 K), differences in the material quality do not affect the linewidth significantly, and under these conditions the PL linewidth is a good measure of the sheet carrier density. The ratio of the 77 K to 4.2 K PL linewidths provides useful information about the crystalline quality of the MDQW structures as illustrated by the correlation with 77 K Hall mobility data and a simple model. We present results of Electron Beam Electroreflectance (EBER) to characterize MDQWs and undoped quantum wells in the AlGaAs/InGaAs/GaAs material system. Several transitions have been observed and fitted to excitonic Lorentzian lineshapes, providing accurate estimates of transition energy and broadening parameter at temperatures of 96 K and 300 K.     

High-resolution X-ray diffraction study of strained InGaAsP/InP multiple quantum well structures grown using all solid sources

This paper reports characterization of n-type strained InGaAsP/InP multiple quantum well (MQW) structures, grown by solid source molecular beam epitaxy (MBE), using high-resolution X-ray diffraction. It was found that well-defined periodic satellite peaks up to 20 orders and the Pendellösung fringes appeared between the satellite peaks were observable, indicating a very high crystalline quality of the MQW structures. The data extracted from the rocking curves, including position and FWHM of the zero-order peak, the angle separation between diffraction peaks and the intensity of the first-order peak, indicate that high-quality InGaAsP/InP MQW structures with controllable well width and sharp interfaces can be successfully grown using all solid sources, and the well width has no significant effect on the quality of the interfaces. These observations are in good agreement with the simulated results using dynamical X-ray theory.     

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.     

Effects of growth interruption on the evolution of InAs/InP self-assembled quantum dots

We investigated the change in the structural and optical properties of InAs/InP quantum structures during growth interruption (GI) for various times and under various atmospheres in metalorganic chemical vapor deposition. Under AsH₃ + H₂ atmosphere, the mass transport for the 2D-to-3D transition was observed during the GI. Photoluminescence peaks from both quantum dots (QDs) and quantum wells were observed from the premature QD samples. The fully developed QDs showed the two distinct temperature regimes in the PL peak position, full width at half maximum (FWHM) and wavelength-integrated peak intensity. The two characteristic activation energies were obtained from the InAs/InP QDs: ∼10 meV for intra-dot excitation and 90 ∼ 110 meV for the excitation out of the dots, respectively. It was also observed that the QD evolution kinetics could be suppressed in PH₃ + H₂ and H₂ atmospheres. The proper control of GI time and atmosphere might be a useful tool to further improve the properties of QDs.     

多层InAs量子点的光致发光研究

采用MBE设备生长了多层InAs/GaAs量子点结构,测量了其变温光致发光谱和时间分辨光致发光谱.结果表明多层量子点结构有利于减小发光峰的半高宽,并且可以提高发光峰半高宽和发光寿命的温度稳定性.实验发现,加InGaAs盖层后,量子点发光峰的半高宽进一步减小,最小达到23.6 meV,并且发光峰出现红移.原因可能在于InGaAs盖层减小了InAs岛所受的应力,阻止了In组分的偏析,提高了InAs量子点尺寸分布的均匀性和质量,导致载流子在不同量子点中的迁移效应减弱.     

Materials characteristics of pseudomorphic high electron mobility transistor structures with InxGa1−xas single quantum well and GaAs-InxGa1−xas (0.25 < x < 0.4) thin strained superlattice active layers

Growth and characterization results are presented for pseudomorphic high electron mobility transistor structures with In_xGa_1-xAs single quantum well and GaAs(h ₁)In _x Ga_1−x As(h ₂) thin strained superlattice active layers where 0.25≤x ≤ 0.4. All of the samples were grown by molecular beam epitaxy. Hall effect at 77 K, photoluminescence at 2 K, in-situ reflection high energy electron diffraction, and transmission electron microscopy measurements are discussed. Critical layer thickness measurements are compared with the Matthews-Blakeslee theory. Photoluminescence transition energies are compared with a self-consistent solution to Schrodinger’s and Poisson’s equations.     

1.3μm低阈值InGaAsP/InP应变补偿MQW激光器的LP-MOCVD生长

报道了用低压金属有机物化学气相淀积（ＬＰ－ＭＯＣＶＤ）方法外延生长ＩｎＧａＡｓＰ／ＩｎＰ应变补偿多量子阱结构。用此材料制备的掩埋异质结（ＢＨ）条形结构多量子阱激光器具有极低阈值电流４～６ｍＡ。２０～４０℃时特征温度Ｔ０高达６７Ｋ，室温下外量子效率为０．３ｍＷ／ｍＡ。     

InGaAs/GaAs量子阱中自组装InAs量子点的光学性质

在InGaAs/GaAs量子阱中生长了两组InAs量子点样品,用扫描电子显微镜(SEM)测量发现,量子点呈棱状结构,而不是通常的金字塔结构,这是由多层结构的应力传递及InGaAs应变层的各向异性引起的.采用变温光致发光谱(TDPL)和时间分辨谱(TRPL)研究了其光致发光稳态和瞬态特性.研究发现,InGaAs量子阱层可以有效地缓冲InAs量子点中的应变,提高量子点的生长质量,可以在室温下探测到较强的发光峰.在量子阱中生长量子点可以获得室温下1 318 nm的发光,并且使其PL谱的半高宽减小到25 meV.     

Investigation on the emission wavelength of GaInNAs/GaAs strained compressive quantum wells on GaAs substrates

In this paper, we study the effect of the incorporation of nitrogen in strained GaInAs quantum well structures. We evaluate the influence of nitrogen on the conduction band energy by using the band anticrossing model. The incorporation of nitrogen appears to decrease the bandgap energy and increase the emission wavelength. The reduction of energy is due to the interaction of the energy of the conduction band with the level of nitrogen and more the concentration of nitrogen increases, more the energy of the band gap decreases. On the other hand, the emission wavelength increases, the advantage of the incorporation of nitrogen in such structures is to vary the wavelength between 0.980 and 1.3 μm while exploiting of course the composition of gallium, composition of nitrogen and the thickness of the quantum well. Less temperature insensitive devices are so intended to be fabricated.