Quantum-size effects on the band edge of CdTe clusters in glass

Abstract

The measurement of quantum-size behavior in semiconductor crystals has been examined through an analysis of the size dependence of the semiconductor’s absorption edge. In past studies, there appeared to be little agreement between theory and experiment for very small crystals. In this paper, the effects of crystal-size distribution and tunneling of the carrier wave functions into the quantum well barrier are considered. An analysis of the microstructure size and absorption edge of CdTe clusters in a glass matrix is conducted with samples ranging from 0.16 to 0.8 times the exciton Bohr diameter at the Γ point and from 1 to 5 times the exciton Bohr diameter at the L point. Results show fully coupled exciton behavior at the L point and a more complex process at the Γ point. In the latter, the band-gap energy increase with decreasing cluster size is significantly smaller than that calculated using a model in which the photoexcited carriers are assumed to be confined to a monosize set of clusters bounded by an infinite potential well. Analysis presented here shows that this discrepancy can be explained in part by inhomogeneous broadening of the absorptive transition and by carrier penetration into the insulator. The quantum-size behavior of CdTe crystals at the Γ point is subsequently found to follow fully decoupled carrier behavior modeled by Efros and Efros [Sov. Phys. Semicond. 16, 772 (1982)] when the inhomogeneous broadening and tunneling effects are taken into account.

Size-dependent photo-induced shift of the first exciton band in CdTe quantum dots in glass prepared by a two-stage heat-treatment process

“…The behavior in three dimensions is in agreement with the results in Fig. 2 [12]. We now compare the results in Fig.…”

Raman spectroscopy of optical phonon confinement in nanostructured materials

“…1 -7 Although a prediction about the potential of nanotechnology was made as early as 1959, 8 the technological applications grew only when some understanding of the fundamental properties of the materials as a function of grain/particle size evolved during the 1980s and the 1990s. Nanostructured materials are generally synthesized in a number of forms: as isolated or loosely connected nanoparticles in the form of powder, 9 as composites of nanoparticles dispersed in a host, 10 or as a compact collection of nano-grains as pellets 11 or thin films. 12 Though in principle one can define a nanostructured Ł Correspondence to: Akhilesh K. Arora, Materials Science Division, Indira Gandhi Centre for Atomic Research, Kalpakkam 603102, India.…”

Quantum confinement, carrier dynamics and interfacial processes in nanostructured direct/indirect-gap semiconductor-glass composites

“…Regarding the fundamental issues, we have observed changes in bandgap energy with cluster size which do not adhere to conventional models at small crystal sizes [1] and appear to depend strongly on whether the semiconductor is a 2-6 direct-gap type or a column 4 indirect-gap type. Here, we have observed that composites doped with CdTe, CdS and CdSe in a silica matrix exhibit a pronounced saturation of the predicted blue shift in bandgap energy with decreasing size [2].…”

“…Materials science issues involved fabrication processes which lead to a variety of cluster sizes and size distributions [1], and interface structures. Potential applications range from very highly efficient solar cells [6] to fast optical switches.…”