Single quantum well

Another strategy reported by Sales links back to the superlattices discussed in Section 7.2.1.4. It was suggested by Mildred Dresselhaus s group at MIT (Hicks et al. 1993) that semiconductor quantum wells would have enhanced figures of merit compared with the same semiconductor in bulk form. PbTe quantum wells were confined by suitable intervening barrier layers. From the results, ZT values of 2 were estimated from single quantum wells. This piece of research shows the intimate links often found nowadays between apparently quite distinct functional features in materials. 

Chang, Y.-M., Lin, H. H., Chia, C. T. and Chen, Y. F. (2004) Observation of coherent interfacial optical phonons in GalnP/ GaAs/GalnP single quantum wells. Appl. Phys. Lett., 84, 2548-2550. 

Figure 41 Left panel calculated 62 first asymmetric peak (- - -) and its Gaussian fit (—) for the (a) Sip]-SiC>2, (b) Si[2]-SiC>2 and (c) S1O2 superlattices. The letter I indicates the interface Gaussian band while the letter Q indicates the bulk-like Gaussian band. Right panel PL spectra of c-Si/Si02 single quantum wells under 488 nm laser excitation at 2 K (a) 1.7 nm, (b) 1.3 nm and (c) 0.6 nm thickness. The asymmetric PL spectra can be fitted by two Gaussian bands, the weak Q band and the strong I band [51],...

Electrically detected magnetic resonance (EDMR) is conceptually similar to ODMR, i.e. the magnetic resonance is observed through spin-dependent electrical rather than optical properties of a sample. Virtually all of the EDMR in GaN-based materials reported to date has bear performed on LEDs and so the device type will serve as a basis for the organisation of this section. Three basic device types have been studied m-i-n-n+ diodes, double heterostructures (DHs) and single quantum wells (SQWs). Some details on these structures can be found elsewhere in this volume [35] and in the original work. 

Recently, LEDs based on emission from an undoped single quantum well (SQW) have been introduced [47],... 

FIGURE 1 Valence subband structures of the unstrained wurtzite GaN/Al02Gao8N single quantum wells, with the well lengths Lz being (a) 30 A, and (b) 50 A... 

FIGURE 5 Valence subband structure of strained wurtzite GaN/Al02GaogN single quantum wells, with 1.0% uniaxial tensile strain along the x-direction, along (a) the ka and (b) the ky directions,... 

FIGURE 6 Valence subband structures of the strained zincblende GaN/Alo2Gao 8N single quantum wells with (a) 0.5% compressive, and (b) 0.2% tensile biaxial strains, with the well length Lz being 40 A. 

FIGURE 1 (a) Optical gain of wurtzite and zincblende bulk GaN. (b) Optical gain of wurtzite bulk GaN and wurtzite GaN/Alo.2Gao gN single quantum wells with well lengths Lz being 60 A. 

FIGURE 4 Optical gain of unstrained zincblende GaN/Alo 2Ga<> N single quantum wells with well length Lz being 60 A The solid and dotted lines stand for the results for TE- and TM-modes. respectively. 

Charge carriers in semiconductors can be confined in one spatial dimension (ID), two spatial dimensions (2D), or three spatial dimensions (3D). These regimes are termed quantum films, quantum wires, and quantum dots as illustrated in Fig. 9.1. Quantum films are commonly referred to as single quantum wells, multiple quantum wells or superlattices, depending on the specific number, thickness, and configuration of the thin films. These structures are produced by molecular beam epitaxy (MBE) and metalorganic chemical vapor deposition (MOCVD) [2j. The three-dimensional quantum dots are usually produced through the synthesis of small colloidal particles. 

Time-resolved measurements of electron transfer times for quantum well photoelectrodes which can be compared with hot electron relaxation times, have not yet been reported. Only some excitation spectra, i.e. photocurrent vs. photon energy for MQWs and single quantum wells (SQWs), have been published so far [2]. In both cases, the photocurrent spectra show distinct structures corresponding to transitions between the hole and electron wells as shown for SQW electrodes in Fig. 9.32. The... 

Fig. 9. 32 Photocurrent action spectrum for GaAs single quantum well (SOW) electrodes at room temperature as a function of inner barrier thickness, Lf. a) L, = 170 A b) = 1.5 pm c) L, = 2.5 pm. For all three samples, the outer barrier thickness is 270 A and the nominal well width is 130 A. For (a) and (b), the peak at about 1.43 eV is due to the GaAs buffer layer. The zero baseline for curve (a) is offset for clarity. (After ref. [79])...

Fig. 9.33 a) Single quantum well (SOW) electrode structure (not to scale) b) energy level diagram for SQW under reverse bias. 

In this chapter we review the work done in our laboratory on the structure (Part II), optical absorption (Part III), photoluminescence (Part IV), and electrical transport (Part V) of a-Si H/a-SiNjci H superlattices. Results with single quantum well structures are discussed by Kukimoto in Chapter 12 of Volume 2ID. 

Quantum well semiconductor lasers with both single and multiple active layers have been fabricated. Quantum well lasers with one active are called single-quantum-well (SQW) lasers and lasers with multiple quantum well active regions are called multiquantum-well (MQW) lasers. The layers separating the active layers in a multiquantum well structure are called barrier layers. Typical examples of the energy band diagram of both SQW and MQW are schematically represented in Fig. 18. 

The active-layer thickness of an SQW laser is typically less than 10 nm, which is to be compared to 0.1 /xm for a DH laser. The threshold current for a typical SQW laser is typically less than 1 mA, while DH structures have threshold currents of several tens of milliamperes. The spectral width of the lasing emission from an SQW laser is usually less than 10 MHz as compared to 100 MHz for a typical DH structure. The output power from single quantum well laser is on the order of 100 mW, although... 

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