Gain and threshold properties of InGaAsN/GaAsN material system for 1.3-μm semiconductor lasers

The gain properties and valence subbands of InGaAsN/GaAsN quantum-well structures are numerically investigated with a self-consistent LASTIP simulation program. The simulation results show that the InGaAsN/GaAsN has lower transparency carrier density than the conventional InGaAsP/InP material system for 1.3-μm semiconductor lasers. The material gain and radiative current density of InGaAsN/GaAsN with different compressive strains in quantum well and tensile strains in barrier are also studied. The material gain and radiative current density as functions of strain in quantum well and barrier are determined. The simulation results suggest that the laser performance and Auger recombination rate of the 1.3-μm InGaAsN semiconductor laser may be markedly improved when the traditional GaAs barriers are replaced with the AlGaAs graded barriers.     

Modulation-doping in 3–5 μm GaAs/AlAs/AlGaAs double barrier quantum well infrared photodetectors: an alternative to achieve high photovoltaic performance and high temperature detection

In this work we propose new detector designs, which allow achieving mid-infrared photovoltaic (PV) detection at temperatures as high as 180 K. The devices, which are grown by molecular beam epitaxy, are modulation-doped (MD) double barrier quantum well infrared photodetectors (QWIPs) based on AlGaAs/AlAs/GaAs. As the photocurrent spectra and I–V characteristics (in the dark and under infrared illumination) show that the dopant location is a relevant design parameter regarding the performance of PV QWIPs, we begin our work with a comparison of the performance of a set of MD samples (where we have varied the dopant location in the AlGaAs barriers) with respect to a well-doped sample of nominally the same structure. We find that the responsivity and detectivity of the MD devices seem to be higher than those of the well-doped detector, specially when the dopant is located in the substrate-sided barrier. Then, in order to improve the dark current-limited performance, we designed a new set of substrated-sided MD detectors that exhibit an extremely low dark current, even at high temperatures, otherwise no drop in the zero bias peak responsivity. Therefore, the association of the notable PV signal detection in the 3–5 μm range of these MD detectors together with the dark current reduction of the new structures has allowed us to achieve a 140 K zero bias peak responsivity of 0.015 A/W and a 180 K zero bias peak responsivity of 0.01 A/W at 4.4 μm.     

A study of GaInP/GaAs interfaces: metallurgical coupling of successive quantum wells

We present a study of GaInP/GaAs interfaces by means of photoluminescence (PL) of multi quantum wells (MQW), embedded in GaInP, or asymmetric structures having an AlGaAs barrier GaInP/GaAs/AlGaAs. The PL energies of quantum wells were compared with calculations based on the transfer matrix envelope function approximation, well suited for asymmetric structures. GaInP/GaAs/AlGaAs MQW structures (GaInP grown first) are in reasonably good agreement with calculations. Reverse ones, AlGaAs/GaAs/GaInP, present a lower PL energy than calculated. But the agreement with theory is recovered on single quantum well samples, or in MQW when the GaInP thickness is increased up to 100 nm. We interpret this phenomenon as a diffusion of arsenic atoms from the next GaAs well through the GaInP barrier. Arsenic atoms exchange with phosphorus atoms at the GaInP-on-GaAs interface of the former well, leading to a small gap strained InGaAs region responsible for the lowering of PL energies.     

GaAsN/GaAs量子阱在1 MeV电子束辐照下的退化规律

为研究GaAsN/GaAs量子阱在电子束辐照下的退化规律与机制,对GaAsN/GaAs量子阱进行了不同注量(1×1015,1×1016 e/cm2)1 MeV电子束辐照和辐照后不同温度退火(650,750,850℃)试验,并结合Mulassis仿真和GaAs能带模型图对其分析讨论。结果表明,随着电子注量的增加,GaAsN/GaAs量子阱光学性能急剧降低,注量为1×1015 e/cm2和1×1016 e/cm2的电子束辐照后,GaAsN/GaAs量子阱PL强度分别衰减为初始值的85%和29%。GaAsN/GaAs量子阱电子辐照后650℃退火5 min,样品PL强度恢复到初始值,材料带隙没有发生变化。GaAsN/GaAs量子阱辐照后750℃和850℃各退火5 min后,样品PL强度随退火温度的升高不断减小,同时N原子外扩散使得样品带隙发生约4 nm蓝移。退火温度升高没有造成带隙更大的蓝移,这是由于进一步的温度升高产生了新的N—As间隙缺陷,抑制了N原子外扩散,同时导致GaAsN/GaAs量子阱光学性能退化。     

Quantum structures for multiband photon detection

The work describes multiband photon detectors based on semiconductor micro-and nano-structures. The devices considered include quantum dot, homojunction, and heterojunction structures. In the quantum dot structures, transitions are from one state to another, while free carrier absorption and internal photoemission play the dominant role in homo or heterojunction detectors. Quantum dots-in-a-well (DWELL) detectors can tailor the response wavelength by varying the size of the well. A tunnelling quantum dot infrared photodetector (T-QDIP) could operate at room temperature by blocking the dark current except in the case of resonance. Photoexcited carriers are selectively collected from InGaAs quantum dots by resonant tunnelling, while the dark current is blocked by AlGaAs/InGaAs tunnelling barriers placed in the structure. A two-colour infrared detector with photoresponse peaks at ∼6 and ∼17 μm at room temperature will be discussed. A homojunction or heterojunction interfacial workfunction internal photoemission (HIWIP or HEIWIP) infrared detector, formed by a doped emitter layer, and an intrinsic layer acting as the barrier followed by another highly doped contact layer, can detect near infrared (NIR) photons due to interband transitions and mid/far infrared (MIR/FIR) radiation due to intraband transitions. The threshold wavelength of the interband response depends on the band gap of the barrier material, and the MIR/FIR response due to intraband transitions can be tailored by adjusting the band offset between the emitter and the barrier. GaAs/AlGaAs will provide NIR and MIR/FIR dual band response, and with GaN/AlGaN structures the detection capability can be extended into the ultraviolet region. These detectors are useful in numerous applications such as environmental monitoring, medical diagnosis, battlefield-imaging, space astronomy applications, mine detection, and remote-sensing. The paper presented there appears in Infrared Photoelectronics, edited by Antoni Rogalski, Eustace L. Dereniak, Fiodor F. Sizov, Proc. SPIE Vol. 5957, 59570W (2005).     

The photocurrent of resonant tunneling diode controlled by the charging effects of quantum dots

We experimentally studied the photocurrent of AlAs/GaAs/AlAs double barrier resonant tunneling diode (RTD), which is composed of an InAs layer of self-assembled quantum-dots on top of AlAs barrier layer. It is found that the charging InAs quantum dots can effectively modulate the carrier transport properties of the RTD. Moreover, we also found that the resonant tunneling current through a single energy level of an individual quantum dot is extremely sensitive to the photo-excited holes bound nearby the dot, and the presence of the holes lowers the electrostatic energy of the quantum dot state. In addition, it is also observed that the photocurrent behaves like step way with the individual photon pulse excitation when the illumination is low enough. The experiment results well demonstrated the quantum amplified characteristics of the device.     

Collective behavior of interwell excitons in GaAs/AlGaAs double quantum wells

Photoluminescence spectra of interwell excitons in double GaAs/AlGaAs quantum wells (n-i-n structures) have been investigated (an interwell exciton in these systems is an electron-hole pair spatially separated by a narrow AlAs barrier). Under resonance excitation by circularly polarized light, the luminescence line of interwell excitons exhibits a significant narrowing and a drastic increase in the degree of circular polarization of photoluminescence with increasing exciton concentration. It is found that the radiative recombination rate significantly increases under these conditions. This phenomenon is observed at temperatures lower than the critical point and can be interpreted in terms of the collective behavior of interwell excitons.     

双量子阱中的子带光吸收

由于微制造技术的不断发展,如液相外延(LPE),气相外延(VPE),金属有机化学气相沉积(MOCVD)以及分子束外延技术(MBE)等先进的材料生长技术方法也日趋完善,从而使得各种低维半导体量子器件(如半导体、超晶格、量子阱、量子线和量子点等)制造日趋成熟。由于这些低维半导体量子器件具有很强的非线性光效应,而且随着材料、外形、尺寸等的不同,非线性光效应也有很大的差别,更由于其可能存在的广泛的应用前景,所以近年来,一直是人们研究的重点。近来,由于人们相信,利用GaAs／AlGaAs量子阱有可能制造出一些新型的光学仪器,如光开关、光限幅器、光调制器等,所以,对不同势形的GaAs／AlGaAs量子阱的非线性光学特性一直吸引着人们进行理论和实验的研究。而在最近几年,对双量子阱的研究也成为了人们的研究重点。通过密度矩阵和迭代的方法,得到双量子阱中的第一、第三阶子带光吸收表达式,我们将用一个典型的GaAs／AlGaAs双量子阱代入其中进行数值计算,并进行讨论。我们的计算结果显示,阱的光吸收峰不但与中间的势垒宽度有关,更与入射光强有关。     

Influence of thin AlAs layer insertion on intersubband optical transitions in GaAs/AlGaAs quantum- well structures

In this work, we demonstrate the thin AlAs layer insertion into GaAs/AlGaAs quantum well (QW) structures and its influence in energy transition in the frequency range of mid-infrared. To realize the more accurate calculation, the graded interface model of QW structures is integrated into our self-consistent solving of Schrodinger and Poisson equations to obtain the energy level and envelope wave functions of QW. We find the thin AlAs layer inserted at various positions in the well can obviously tune intersubband optical transitions. The corresponding tuning range can be 50 meV. We find that the thicker AlAs layer (2 monolayers) can provide wider tuning range and larger oscillator strength between subbands 1 and 3, compared with the thinner one (1 monolayer). Our results suggest that thin semiconductor layer may be an idea optimization design for the quantum well terahertz lasers which are based on optical pumping with mid-infrared lasers.     

Reduction in relaxation time due to ionized impurities in GaAs/AlGaAs quantum well structures

Time-resolved photoluminescence measurements in δ -doped GaAs/AlGaAs on the quantum well structures are performed to study effects of ionized impurities relaxation process of photoexcited carriers. It is theoretically shown that a thin quantum well with a δ -doping layer inserted in the barrier layer of double quantum wells enhances the impurity scattering rate significantly. Photoluminescence decay time in the δ -doped samples is found to decrease compared with the undoped samples.     

Optical characterization of InGaAsN/GaAsN/GaAs quantum wells with InGaP cladding layers

Optical properties of InGaAsN/GaAs and InGaAsN/GaAsN/GaAs quantum well structures with InGaP cladding layers were studied by photoreflectance at various temperatures. The excitonic interband transitions of the InGaAsN/GaAsN/GaAs QW systems were observed in the spectral range above hν=E_g(InGaAsN). The confinement potential of the system with strain compensating GaAsN barriers became one step broader, thus more quantum states and larger optical transition rate were observed. A matrix transfer algorithm was used to calculate the subband energies numerically. Band gap energies, effective masses were adopted from the band anti-crossing model with band-offset values adjusted to obtain the subband energies to best fit the observed optical transition features. A spectral feature below and near the GaAs band gap energy from GaAs barriers is enhanced by the GaAs/InGaP interface space charge accumulation induced internal field.     

GaAs quantum well structures investigation by local cathodoluminescence

The article shows the cathodoluminescence technique application to a quality analysis of a semiconductor multilayer heterostructures. Two structures with a GaAs quantum well embedded between the AlGaAs and GaInP barriers were investigated. The AlGaAs/GaAs/GaInP and GaInP/GaAs/AlGaAs structures were grown by MOCVD on a GaAs substrate. In this work we study the interface quality of quantum-dimensional GaAs layer by means of the local cathodoluminescence. Degradation and broadening of GaAs/GaInP interface occurring during the growth process of GaAs on GaInP layer was assumed to result in the formation of a layer with mixed composition at the interface. In addition, the presence of the layer prevented the formation of a quantum well in the GaAs layer. The transition layer was clearly observed by the cathodoluminescence. In the other case it was found that the growth of a structure with GaAs layer on top of AlGaAs produced a quantum well with a 10 nm thickness. The interface quality and layer thicknesses were also confirmed by the X-ray diffraction investigation of these structures.     

Comparative Study of the Two-Dimensional Plasma Excitations in the Heterostructures ZnO/MgZnO,AlAs/AlGaAs,and GaAs/AlGaAs

The plasma oscillations in new advanced two-dimensional electron systems (2DESs) based on the heterostructures ZnO/MgZnO, AlAs/AlGaAs, and GaAs/AlGaAs are studied and compared. The relaxation times and the effective masses in samples with various electron densities in these 2DESs are found by microwave plasma spectroscopy. The specific features of the plasma oscillations in the AlAs/AlGaAs quantum wells that are induced by the filling of several valleys with electrons are revealed. The possibility of adjusting a plasmon spectrum via changing the electron concentrations in valleys is demonstrated.     

Quantum box resonant tunneling spectroscopy: Experiments and modelisation

We have calculated the potential profile and the electronic levels in resonant tunneling double barrier structures with nanometric lateral dimensions (≤ 500 nm) for various contact doping. At biases for which the box states (laterally confined quantum well) are resonant with the emitter Fermi level, fine structures are expected in the resonant tunneling current. Comparison with I(V) characteristics measured on nanometric GaAs/GaAlAs and GaAs/GaAlAs/InGaAs resonant tunneling diodes shows that our model accounts for the resonance bias voltage and explains the shape of the current peak. The fine structure observed in the current peak provides a spectroscopy of the confined states in the quantum box.     

Far-infrared absorption studies of Be acceptors in δ-doped GaAs/AlAs multiple quantum wells

We report a far-infrared absorption study of internal transitions of shallow Be acceptors in both bulk GaAs and a series of δ-doped GaAs/AlAs multiple quantum well samples with well thicknesses of 20, 15 and 10 nm. Low temperature far-infrared absorption measurements clearly show three principal absorption lines due to transitions of Beacceptor states from the ground state to the first three odd-parity excited states, respectively. Using a variational principle, the 2p-1s transition energies of quantum confined Be acceptors are calculated as a function of the well width. It is found that the theoretical calculation of the 2p_z → 1s transitions is in good agreement with the D-like line experimental data.     

Linear and nonlinear intersubband optical absorption in symmetric double semi-parabolic quantum wells

The linear and the nonlinear intersubband optical absorption in the symmetric double semi-parabolic quantum wells are investigated for typical GaAs/AlxGa1−xAs. Energy eigenvalues and eigenfunctions of an electron confined in finite potential double quantum wells are calculated by numerical methods from Schrödinger equation. Optical properties are obtained using the compact density matrix approach. In this work, the effects of the barrier width, the well width and the incident optical intensity on the optical properties of the symmetric double semi-parabolic quantum wells are investigated. Our results show that not only optical incident intensity but also structure parameters such as the barrier and the well width really affect the optical characteristics of these structures.     

Interwell excitons in GaAs/AlGaAs double quantum wells and their collective properties

Luminescence spectra of interwell excitons in GaAs/AlGaAs double quantum wells with electric-field-tilted bands (n-i-n) structures were studied. In these structures the electron and the hole in the interwell exciton are spatially separated between neighboring quantum wells by a narrow AlAs barrier. Under resonant excitation by circularly polarized light the luminescence line of the interwell excitons exhibited appreciable narrowing as their concentration increased and the degree of circular polarization of the photoluminescence increased substantially. Under resonant excitation by linearly polarized light the alignment of the interwell excitons increased as a threshold process with increasing optical pumping. By analyzing time-resolved spectra and the kinetics of the photoluminescence intensity under pulsed excitation it was established that under these conditions the rate of radiative recombination increases substantially. The observed effect occurs at below-critical temperatures and is interpreted in terms of the collective behavior of the interwell excitons. Studies of the luminescence spectra in a magnetic field showed that the collective exciton phase is dielectric and in this phase the interwell excitons retain their individual properties.     

(CdSe)1(ZnSe)3/ZnSe短周期超晶格多量子阱的共振Ramam谱

在(CdSe)₁(ZnSe)₃/ZnSe短周期超晶格多量子阱中,根据一维线性链模型计算的结果与实验结果的比较表明,我们在不同的共振条件下分别观察到了来自多量子阱的阱中和垒中ZnSe限制纵光学声子模的Raman散射。与GaAs/AlAs量子阱的偏振选择定则不同,在共振条件下,我们在两种偏振配置下都观察到了阱中ZnSe限制模LO₁,并认为这种不同可能来源于样品特殊的电子子带结构和光学声子行为。 关键词：     

Real-space transfer by hot electron resonant tunneling

Demonstrations of real-space transfer transistors have primarily shown real-space transfer current due to thermionic emission of heated channel electrons over low heterostructure barriers. In this paper we demonstrate real-space transfer of hot electrons due to resonant tunneling through multiple AlAs/GaAs/AlAs double barrier structures.