We present photoluminescence (PL) studies of GaN and ZnO nanocrystallites and powders. Our studies show that in addition to the intrinsic photoluminescence characteristics, the photoluminescence properties of the porous media are also a strong function of conditions such as ensemble size and powder density, ultraviolet-laser excitation power, and vacuum state. PL redshifts up to 120 meV were observed for GaN and ZnO crystallites and were attributed to laser heating and heat trapping in the ensemble. The electron-phonon interaction model for GaN indicated ensemble temperature ∼550 K, which is consistent with the finding obtained via high-temperature PL and Raman experiments. The PL in the vacuum state exhibited a significant redshift, ∼80 meV relative to that in air, and the PL of a dense ZnO pellet was found to resemble that of the bulk more than does a loose powder. The PL analyses indicated an excitonic emission at room temperature for both GaN and ZnO crystallites with intensity saturation occurring fo...

Photoluminescence dynamics in ensembles of wide-band-gap nanocrystallites and powders

Free-standing ternary InGaAs nanowires (NW) are at the core of intense investigations due to their integration capabilities on silicon (Si) for next-generation photovoltaics, integrated photonics, tunneling devices, and high-performance gate all-round III–V/Si NW transistors. In this review, recent progress on the growth, structural, optical and electrical properties of InGaAs NWs on Si substrate is highlighted. Particular focus is on a comparison between conventional catalyst-assisted and catalyst-free growth methods as well as self-assembled versus site-selectively grown NW arrays. It will be shown that catalyst-free, high-periodicity NW arrays with extremely high compositional uniformity are mandatory to allow un-ambiguous structure–property correlation measurements. Here, interesting insights into the electronic/optical properties of wurtzite, zincblende and mixed crystal phases of InGaAs will be highlighted based on recent photoluminescence spectroscopy data. Finally, the InGaAs NW-on-Si system is also discussed in the realms of heterojunction properties, providing a promising system for steep-slope tunneling field effect transistors in future low-power post-CMOS intergrated microelectronics and broad-band photoabsorption and detec-tion devices. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Growth and properties of InGaAs nanowires on silicon

A photoluminescence study of polycrystalline thin-film CdTe/CdS solar cells

Photoluminescence (PL) spectra of detector-grade Cd 1-x Zn x Te crystals with x = 0.07 to 0.14 were measured as a function of the excitation laser power and over the temperature range from 12 to 295 K. Two bound exciton transitions at the energies of 13 and 24 meV below the band-gap E g and a number of phonon replicas dominate the low-temperature PL spectra. The transition at the energy of E g - 13 meV is attributed to a neutral donor-bound exciton D 0 X. The excitation power and temperature dependence of the peak at the energy of E g - 24 meV show that it is of excitonic origin with binding energy of 13 meV. The intensity of this A 0 X peak is found to depend on z, which suggests that it is related to structural defects. In some samples a donor-acceptor pair (DAP) transition at the energy of E g - 60 meV is observed. The PL spectra also exhibit a weak, defect-related broad peak at the energy of about E g - 200 meV. The PL of a large number of samples from different boules and locations in the boules is compared. The DAP-peak intensity was observed to depend strongly on the boule.

Photoluminescence of Cd1-xZnxTe crystals grown by high-pressure Bridgman technique

R. R. Lieten,1,2,3,* K. Bustillo,4 T. Smets,1 E. Simoen,3 J. W. Ager III,2 E. E. Haller,2,4 and J.-P. Locquet1 1Department of Physics and Astronomy, K.U. Leuven, 3001 Leuven, Belgium 2Division of Materials Sciences, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA 3IMEC, 3001 Leuven, Belgium 4Department of Materials Science and Engineering, University of California, Berkeley, California 94720, USA (Received 25 April 2012; published 9 July 2012)

Photoluminescence of bulk germanium

Photoluminescence spectroscopy of excitons for evaluation of high-quality CdTe crystals

Spatial origin of various PL lines in CdTe at 77 K

Time-resolved and steady-state photoluminescence (PL) data on excitonic polaritons in CdTe are presented and analyzed in terms of polariton formation, transport, and relaxation processes. The sample-to-sample variation in the polariton line shape and the shapes of the various polariton phonon sideband indicates that there is substantial polariton emission from below the bottleneck region, which shows that transport effects dominate the polariton line shape. Time-resolved PL data from the polariton band show that both formation and decay rates vary with time and k state, producing complex polariton decay waveforms. Polariton formation at the bottom of the band persists for up to 3 ns after optical excitation. Bound-exciton lifetimes can be extracted from the bound-exciton PL decay waveforms if the time dependence of the binding-polariton population is known. These results are compared with previous experimental and theoretical studies of polariton dynamics.

Exciton-polariton dynamics and photoluminescence line shapes in cadmium telluride.

Spectrally filtered cathodoluminescence of CdTeL.O. Bubulac, J. Bajaj, W.E. Tennant and P.R. NewmanRockwell International Science Center, 1049 Camino Dos Rios, Thousand Oaks, CA 91360AbstractThe imaging cathodoluminescence capability of a scanning electron microscope has beencomplemented by a spectral filtering technique to study the spatial origin of photolumi-nescence from CdTe at 77K. The intent of this work is to resolve the spatial origin ofdifferent luminescence spectral components in different regions of the crystal (e.g., mid -grain, near -grain boundary, etc.). The results indicate different spatial locations forthe exciton and the defect photoluminescence lines, and the association of bound excitonlines with clustered dislocations. Furthermore, the exciton line appears to originatefrom two different regions of the sample, which may imply bound excitons from twodifferent binding sites.We infer from the present study that the criterion generally adopted, that a highbound exciton band intensity and a relatively low defect band intensity implies goodcrystal quality, may be ambiguous.IntroductionCdTe is a very important II -VI semiconductor for infrared detection. This material isgenerally used as a substrate for epitaxial growth of HgCdTe. It has been demonstratedthat the properties of HgCdTe strongly depend on the quality of CdTe substrates. There-fore, there is a need to develop techniques to characterize CdTe. Several techniques suchas photoluminescence (PL)1'2 and cathodoluminescence (CL)3

P. R. Newman

Papers

Photoluminescence spectroscopy of excitons for evaluation of high-quality CdTe crystals

Spatial origin of various PL lines in CdTe at 77 K

Exciton-polariton dynamics and photoluminescence line shapes in cadmium telluride.

Spectrally Filtered Cathodoluminescence Of CdTe