Dark currents of GaAs/AlGaAs quantum-well infrared photodetectors

We study the dark current of the GaAs/AlGaAs quantum-well infrared photodetector (QWIP) by assuming a drift-diffusion carrier transport in the barriers where the electric fields are obtained by the current continuity condition and the self-consistent energy band structure. It has been shown that due to the current continuity condition, the dark currents across the QWIP devices are determined by the thermionic emission from the emitter to the multiple quantum well (MQW) region. The self-consistent calculation of the Schrödinger and Poisson equations shows a weak electric field in the barrier region connecting to the emitter (much smaller than the average field across the QWIP at low bias) due to the accumulation of carriers in the triangle quantum well formed at the emitter-MQW interface, which results in a very small dark current at low bias. The numerical results explain well our experimental observation.     

Influence of europium doping on the sensitization of luminescence in GaAs/AlGaAs and InGaN/GaN quantum-well structures

A correlation between the photoluminescence spectra and structural parameters of Eu-doped quantum- well nanostructures InGaN/GaN and GaAs/AlGaAs is established. It is shown that the incorporation of rare-earth ions initiates lattice (as a rule, compressive) strains. The excitation migration in structures of high perfection stimulates transfer of nonequilibrium carriers to the ⁵ D ₂-⁵ D ₀ atomic levels of the Eu ion. In less perfect structures, the insertion of a rare-earth ion leads to the formation of isovalent traps in GaN layers capable of effectively capturing nonequilibrium carriers, which increases the intensity of photoluminescence of the structure by one order of magnitude.     

Quantum cascade electroluminescence in GaAs/AlGaAs structures

The operation of a unipolar quantum cascade light-emitting diode based on the material system GaAs/AlGaAs is reported. The LED operates at a wavelength of 6.9 μm. Detailed analysis of the electroluminescence spectra shows a linewidth as narrow as 14 meV at cryogenic temperatures, increasing to 20 meV at room temperature. For typical drive-current densities of 1 kA/cm² the optical output power lies in the ten 10 nW range. Additional absorption and photocurrent measurements provide a complete characterization of the mid-infrared emitter.     

Single quantum well transistor with modulation doped AlGaAs/GaAs/AlGaAs structures

Self-consistent calculations have been performed to obtain the wave functions and energy subbands of the two-dimensional electrons confined in a single quantum well of a Al_xGa_1?xAs/GaAs/Al_xGa_1?xAs heterostructure. The wave functions of the two-dimensional electron gas are found to be easily controlled by an external gate voltage applied between the AlGaAs-barriers, indicating a capability of fabricating a novel quantum well device, a modulation-doped single quantum well transistor.     

Phase diagram of the bose condensation of dipolar excitons in GaAs/AlGaAs quantum-well heterostructures

Experimental studies of the phase diagram of Bose condensation in a system of spatially indirect dipolar excitons in GaAs/AlGaAs quantum wells are reviewed. The properties of spatially periodic patterns arising in the luminescence of the exciton Bose condensate in a ring-shaped potential trap and the coherence of the condensate luminescence are discussed.     

Terahertz injection electroluminescence in multiperiod quantum-cascade AlGaAs/GaAs structures

Terahertz electroluminescence in the range ≈1.5 THz was observed in a quantum-cascade GaAs/AlGaAs structure containing 40 periods of tunnel-coupled wells. The luminescence is caused by the spatially indirect optical electron transitions between the ground states of neighboring quantum wells.     

Electro-optic effects in GaAs/AlGaAs parabolic quantum well structures

We report on a systematic experimental and theoretical investigation of the interband electroabsorption in GaAs/AlGaAs parabolic quantum well (PQW) structures. In our experiments, we performed transmission and reflectance measurements using a sensitive double modulation technique. The measurements were carried out on p–i–n diode type PQW samples with two different well widths. In the sample with the narrow PQW, the discrete structure of the interband subband transitions can be resolved in the electroabsorption spectra. In the sample with the wide PQW, and therefore a small subband spacing, these transitions can no longer be resolved individually due to the broadening. Their superposition, however, results in a red-shifting, quasi-linear pattern in the electroabsorption spectra, which is modulated by the blue-shifting, non-linear fan of the ‘ arabolic Franz–Keldysh effect’. The experimental results are in very good agreement with calculated single-particle absorption spectra based on a simple harmonic oscillator model.     

Exciton cooling and localization in GaAs/AlGaAs multiquantum well structures

We report experimental and theoretical results on picosecond time resolved photoluminescence spectroscopy of 2D-excitons in multiquantum well structures. A theoretical model is formulated which includes the cooling of the free exciton gas by acoustical phonon emission and the localization of excitons due to interface defects. The cooling rate of 2D excitons is shown to be enhanced with respect to the 3D case.     

Aluminium implantation-induced disordering of AlGaAs/GaAs quantum well structures

The process of Al implantation-induced disordering of AlGaAs/GaAs quantum well structures has been studied for optical waveguide applications. A study of the implanted samples using photoluminescence demonstrates that disordering is primarily a damage-based process and that this process may be suitable for the fabrication of surface gratings.     

Resonant magnetopolaron effects in GaAs/AlGaAs multiple quantum well structures

A detailed experimental study of electron cyclotron resonance (CR) has been carried out at 4.2 K in three modulation-doped GaAs/Al_0.3Ga_0.7As multiple quantum well samples in fields up to 30 T. A strong avoided-level-crossing splitting of the CR energies due to resonant magnetopolaron effects is observed for all samples near the GaAs reststrahlen region. Resonant splittings in the region of AlAs-like interface phonon modes of the barriers are observed in two samples with narrower well width and smaller doping concentration. The interaction between electrons and the AlAs interface optical phonon modes has been calculated for our specific sample structures in the framework of the memory-function formalism. The calculated results are in good agreement with the experimental results, which confirms our assignment of the observed splitting near the AlAs-like phonon region is due to the resonant magnetopolaron interaction of electrons in the wells with AlAs-like interface phonons.     

Si杂质扩散诱导InGaAs/AlGaAs量子阱混杂的研究（英文）

光学灾变损伤(COD)常发生于量子阱半导体激光器的前腔面处,极大地影响了激光器的出光功率及寿命。通过杂质诱导量子阱混杂技术使腔面区波长蓝移来制备非吸收窗口是抑制腔面COD的有效手段,也是一种高效率、低成本方法。本文选择了Si杂质作为量子阱混杂的诱导源,使用金属有机化学气相沉积设备生长了InGaAs/AlGaAs量子阱半导体激光器外延结构、Si杂质扩散层及Si 3 N 4保护层。热退火处理后,Si杂质扩散诱导量子阱区和垒区材料互扩散,量子阱禁带变宽,输出波长发生蓝移。退火会影响外延片的表面形貌,而表面形貌则可能会影响后续封装工艺中电极的制备。结合光学显微镜及光致发光谱的测试结果,得到825℃/2 h退火条件下约93 nm的最大波长蓝移量,也证明退火对表面形貌的改变,不会影响波长蓝移效果及后续电极工艺。     

Electroreflectance and photoluminescence measurement of passivation by hydrogenation in GaAs/AlGaAs structures

We have studied by electrolyte electroreflectance and photoluminescence a GaAs/AlGaAs resonant tunneling structure (RTS) with a highly n-doped GaAs cap, before and after hydrogenation. We measured the amount of passivation of shallow donor states and of deep traps in the cap and found the approximate pinning levels and interace charges of the RTS.     

Population inversion study of GaAs/AlGaAs three-quantum-well quantum cascade structures

A population inversion study of GaAs/AlxGa1-x As three-quantum-well quantum cascade structures is presented. We derive the population inversion condition (PIC) of the active region (AR) and discuss the PICs on different structures by changing structural parameters such as the widths of quantum wells or barriers in the AR. For some instances, the PIC can be simplified and is proportional to the spontaneous emission lifetime between the second and the first excited states, whereas some other instances imply that the PIC is proportional to the state lifetime of the second excited state.     

Electro-optical probing of envelope wavefunctions in GaAs/AlGaAs parabolic quantum well structures

We report on a systematic experimental and theoretical study of the interband electroabsorption in GaAs/AlGaAs parabolic quantum well structures. Investigating a sample with an appropriately designed well width, we are able to observe a complex interplay of various electro-optical effects. The obtained results can be interpreted in terms of probing the electric-field dependent overlaps between the harmonic oscillator type envelope wavefunctions of electrons and holes.