Multiple Quantum Well Structure

D.S. Chemla, D.A.B. Miller, and P.W. Smith, Nonlinear Optical Properties of Multiple Quantum Well Structures for Optical Signal Processing... 

Multiple linear regression methods, 16 753 Multiple-lined landfills, 25 877 Multiple liquid-path plates, 8 764 Multiple quantum well structure (MQW), 14 844... 

FIGURE 2 Bright-field transmission electron micrograph of a GalnN/GaN multiple quantum well structure exhibiting V-defects [12],... 

Rosker M. J., Wise F. W. and Tang C. L. (1986), Eemtosecond optical measurement of hot-carrier relaxation in GaAs, AlGaAs, and GaAs/AlGaAs multiple quantum well structures , App/. Phys. Lett. 49, 1726-1728. 

One subject that attracted much attention is the nonlinear optical properties of these semiconductor nanoclusters [17], The primary objective is to find materials with exceptional nonlinear optical response for possible applications such as optical switching and frequency conversion elements. When semiconductors such as GaAs are confined in two dimensions as ultrathin films (commonly referred to as multiple quantum well structures), their optical nonlinearities are enhanced and novel prototype devices can be built [18], The enhancement is attributed mostly to the presence of a sharp exciton absorption band at room temperature due to the quantum confinement effect. Naturally, this raises the expectation on three-dimensionally confined semiconductor nanoclusters. The nonlinearity of interest here is the resonant nonlinearity, which means that light is absorbed by the sample and the magnitude of the nonlinearity is determined by the excited state... 

For bulk semiconductors and multiple quantum well structures (one-dimensional confined semiconductors), transport properties are of great interest and are important for practical applications such as transistors and detectors. Semiconductor nanoclusters are usually confined in three-dimensions by insulating matrices such as polymers and glasses, where the transport of carriers is not feasible. To explore transport-related applications of semiconductor clusters, a matrix that is capable of transporting carriers is needed, In addition, the redox properties of the matrix have to allow injection of carriers from semiconductor nanoclusters to the matrix. 

MODELLING VERTICAL TUNNELING IN SEMICONDUCTOR MULTIPLE QUANTUM WELL STRUCTURES EFFECT OF THE DISORDER IN LAYER PARAMETERS... 

We model the vertical electron transport in semiconductor multiple quantum well structures at low temperatures. A disorder is introduced into the layer parameters, namely, widths or potentials of the quantum wells or barriers. Field-dependent electron transmission spectra and current-voltage charaeteristics are calculated for various types and degrees of the disorder. 

Figure 4.19 Principle of multiple quantum-well structure of a quantum cascade laser (QCL). Top right standard QCL device Alpes Lasers)-, bottom right QCL integrated into common laser unit, including drive electronics and TE cooling (Cascade Technologies)...

Ohmori, Y., Morishima, C., Fujii, A., Yoshida, M., and Yoshida, K., Novel optical and electroluminescent characteristics of organic multiple-quantum-well structure utilizing fluorescent dye molecules. Mol. Cryst. Liq. Cryst., 267, 417-422 (1995). 

Concerning potential applications we considered only all-optical nonlinear effects. It should be mentioned that liquid crystals can be utilized in the so-called self-electrooptic-devices (SEED) too. In these devices there is an electrical feedback of the transmitted light to the layer. Such systems can be constructed by combining a photoconducting layer with a liquid crystal film. Ferroelectric liquid crystals are especially suitable for this purpose and may represent an alternative to the multiple quantum-well structures on which SEED-s are normally based. Whether all-optical effects will find a widespread application is still an open question. 

A more recent trend is to design lasers whose performance parameters are less temperature dependent One way to accomplish this is to change the laser s semiconductor layer structure. For example, a significantly lower temperature dependence is shown in Fig 9.51(b) which is a similar plot to Fig. 9.51(a) but for a laser in which the simple single active layer has been replaced by a multiple quantum well structure. 

In order to improve the emission efficiency of these devices, quantum well structures are introduced for efficient trapping of electron and hole pairs. A quantum well is a multilayered structure where a semiconductor material with a low bandgap (well) is sandwiched between two layers of semiconductor materials with higher bandgap (barriers). A typical InGaN/GaN multiple quantum well structure in a blue InGaN based LED is shown in Figure 9. 

Miller, D. A. B., Chemla, D. S., Eilenberg, D. J., Smith, P W., Gossard, A. C., Tsang, W. T. (1982). Large room-temperature optical nonlinearity in GaAs/Gai-xAljfAs multiple quantum well structures. Applied Physics Letters, 41, 679-681. 

W Xie, DC GriUo, RL Gunshor, M Kobayashi, H Jeon, J Ding, AV Nurmikko, GC Hua, N Otsuka. Room temperature blue light emitting p-n diodes from Zn(S,Se)-based multiple quantum well structures. Appl Phys Lett 60 1999, 1992. 

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