PL and FTIR Absorption Study on Porous Silicon in Situ During Etching, in Oxygen Ambient, and After Chemical Oxidation

1992 ◽  
Vol 283 ◽  
Author(s):  
G. Mauckner ◽  
T. Walter ◽  
T. Baier ◽  
K. Thonke ◽  
R. Sauer Abteilung
Keyword(s):  
Defect Density ◽  
Chemical Oxidation ◽  
Laser Exposure ◽  
Porous Si ◽  
Radiative Recombination Rate ◽  
Time Resolved ◽  
Radiative Defect ◽  
Recombination Lifetimes ◽  
Time Resolved Photoluminescence

ABSTRACTSteady state and time-resolved photoluminescence (PL) and Fourier-transform infrared (FTIR) spectroscopy have been performed in situ during etching, on “as prepared” porous Si in air under laser exposure and on chemically oxidized porous Si. We suppose that PLdegradation of “as prepared” porous Si is caused by creating non-radiative defect centers during photooxidation. Chemically oxidized porous Si shows increased PL intensity and longer recombination lifetimes as compared to non-oxidized samples. We conclude, that an oxide layer with low defect density on the inner surface of chemically oxidized porous Si reduces the non-radiative recombination rate.

Exciton dynamics in thick GaN MOVPE epilayers deposited on sapphire.

1997 ◽  
Vol 2 ◽  
Author(s):  
J. Allègre ◽  
P. Lefebvre ◽  
J. Camassel ◽  
B. Beaumont ◽  
Pierre Gibart
Keyword(s):  
Layer Thickness ◽  
Buffer Layers ◽  
Rate Equations ◽  
Time Resolved ◽  
Versus Layer ◽  
Level Model ◽  
Shallow Impurities ◽  
Aln Buffer ◽  
Time Resolved Photoluminescence

Time-resolved photoluminescence spectra have been recorded on three GaN epitaxial layers of thickness 2.5 μm, 7 μm and 16 μm, at various temperatures ranging from 8K to 300K. The layers were deposited by MOVPE on (0001) sapphire substrates with standard AlN buffer layers. To achieve good homogeneities, the growth was in-situ monitored by laser reflectometry. All GaN layers showed sharp excitonic peaks in cw PL and three excitonic contributions were seen by reflectivity. The recombination dynamics of excitons depends strongly upon the layer thickness. For the thinnest layer, exponential decays with τ ~ 35 ps have been measured for both XA and XB free excitons. For the thickest layer, the decay becomes biexponential with τ1 ~ 80 ps and τ2 ~ 250 ps. These values are preserved up to room temperature. By solving coupled rate equations in a four-level model, this evolution is interpreted in terms of the reduction of density of both shallow impurities and deep traps, versus layer thickness, roughly following a L−1 law.

Robust single-mode lasers based on hexagonal CdS microflakes

2020 ◽  
Vol 8 (32) ◽  
pp. 11201-11208
Author(s):  
Yang Mi ◽  
Yaoyao Wu ◽  
Jinchun Shi ◽  
Sheng-Nian Luo
Keyword(s):  
Radiative Recombination ◽  
Single Mode ◽  
Whispering Gallery Mode ◽  
Radiative Recombination Rate ◽  
Electron Hole ◽  
High Quality ◽  
Time Resolved ◽  
Whispering Gallery ◽  
Electron Hole Plasma ◽  
Time Resolved Photoluminescence

We have achieved single-mode whispering-gallery-mode lasing in CdS microflakes with sharp linewidth (∼0.12 nm) and high quality factor (∼4200). Such lasers are superior to previous CdS lasers in these lasing parameters. Through time-resolved photoluminescence measurements, electron–hole plasma recombination is established to be the lasing mechanism. The radiative recombination rate of CdS microflakes is enhanced by a factor of ∼4.7 due to the Purcell effect.

Optical Transitions and Recombination Lifetimes in GaN and InGaN Epilayers, and InGaN/GaN and GaN/AlGaN Multiple Quantum Wells

1996 ◽  
Vol 449 ◽  
Author(s):  
M. Smith ◽  
J. Y. Lin ◽  
H. X. Jiang ◽  
A. Khan ◽  
Q. Chen ◽  
...  
Keyword(s):  
Quantum Wells ◽  
Chemical Vapor ◽  
Multiple Quantum Wells ◽  
Organic Chemical ◽  
Multiple Quantum ◽  
Optical Transitions ◽  
Time Resolved ◽  
Metal Organic ◽  
Recombination Lifetimes ◽  
Time Resolved Photoluminescence

ABSTRACTTime-resolved photoluminescence (PL) has been employed to study the optical transitions and their dynamical processes in GaN and InxGa1-xN epilayers, and GaN/GaN and GaN/ALxGa1-xN multiple quantum wells (MQW). We compare the results from both metal-organic chemical vapor deposition (MOCVD) and molecular beam epitaxy (MBE) grown samples. In addition, results are also compared with GaAs/ALxGa1-xAs MQW. It was found for all samples that the low temperature emission lines were dominated by radiative recombination transitions of either localized or free excitons, which demonstrates the high quality and purity of these III-nitride materials.

Origin of the Infrared Band From Porous Silicon

1994 ◽  
Vol 358 ◽  
Author(s):  
G. Mauckner ◽  
J. Hamann ◽  
W. Rebitzer ◽  
T. Baier ◽  
K. Thonke ◽  
...  
Keyword(s):  
Exponential Decay ◽  
Porous Si ◽  
Temperature Dependent ◽  
Infrared Band ◽  
Lifetime Distributions ◽  
Time Resolved ◽  
Si Nanocrystals ◽  
Recombination Lifetimes ◽  
Stretched Exponential Decay ◽  
Decay Behavior

ABSTRACTThe photoluminescence (PL) infrared (IR)-band of p-doped porous Si (PS) films is studied by steady-state and time-resolved PL and by photoluminescence excitation (PLE) in detail. In analogy to the S-band in the visible the IR-band shifts to higher energies with reduced average nanocrystal size. The IR- and S-bands are very different in their decay behavior and in their recombination lifetimes. The temperature-dependent PL intensity shows non-exponential decay with lifetime distributions in the nsec-µsec range in contrast to the stretched exponential decay shape of the S-band corresponding to lifetime distributions in the μsec -msec range. The origin of the IR-band is likely related to radiative recombination at deep defects in Si nanocrystals with quantum-upshifted band gaps.

scholarly journals Ultrafast Carrier Dynamics and Recombination in Green Emitting InGaN MQW LED

2006 ◽  
Vol 916 ◽  
Author(s):  
Alexander N. Cartwright ◽  
M. C-K. Cheung ◽  
F. Shahedipour-Sandvik ◽  
J. R. Grandusky ◽  
M. Jamil ◽  
...  
Keyword(s):  
Defect Density ◽  
Optical Transition ◽  
Effective Means ◽  
Green Emission ◽  
Layer Growth ◽  
Layer By Layer ◽  
Green Luminescence ◽  
Time Resolved ◽  
Photoluminescence Decay ◽  
Time Resolved Photoluminescence

AbstractTime-resolved photoluminescence studies can provide useful information for the development of InGaN/GaN heterostructures for long wavelength visible emitters. In this paper, we present results of time-resolved photoluminescence from samples grown using two different approaches to achieve green emission from InGaN/GaN MQWs. In one approach, samples, with high indium incorporation, were grown on a high quality AlN substrate to achieve green emission. The resulting photoluminescence decay of the green luminescence is long-lived and non-exponential. Quantitative analysis showed that the decay has a stretched-exponential characteristic, typical of InGaN/GaN MQW with potential fluctuation along the growth plane. This carrier localization, in a structure with low defect density, proves to be an effective means to achieve green emission. In another approach, a piezoelectric Stark-like ladder effect is used. In this case, a methodical layer-by-layer growth homogeneity optimization process was adopted to achieve an optical transition below the electron to heavy-hole (e1hh1) transition when the quantum well is subjected to the strong piezoelectric polarization dipole. This approach has proven to be successful in achieving green luminescence on conventional sapphire substrates. The resulting photoluminescence decay at 14 K, of a sample grown by this approach, is single exponential and shorter in duration than the decay observed in the first approach. This exponential decay is consistent with previous AFM studies that revealed a homogeneous active region.

Study of 3-MeV electron irradiation damage in amorphous silicon with TRMC

2004 ◽  
Vol 808 ◽  
Author(s):  
A. Klaver ◽  
J.M. Warman ◽  
M.P. de Haas ◽  
J.W. Metselaar ◽  
R.A.C.M.M. van Swaaij
Keyword(s):  
Simple Model ◽  
Amorphous Silicon ◽  
Electron Irradiation ◽  
Probe Beam ◽  
Electron Accelerator ◽  
Defect Density ◽  
Irradiation Damage ◽  
Microwave Conductivity ◽  
Time Resolved

ABSTRACTThe effects of 3-MeV electron irradiation on a-Si:H have been studied using Time-Resolved Microwave Conductivity (TRMC). A Van der Graaff electron accelerator is used to generate the probe-beam pulses for the TRMC experiment as well as for the in-situ irradiation of the samples for the degradation of the material. Using several probe-beam pulse doses, TRMC transients were obtained on samples that have been subjected to various radiation fluences. These transients were later analyzed using a simple model based on the Shockley-Read-Hall capture and emission processes. Using these simulations we deduce a relationship between the radiation fluence and the defect density in the material.

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