Micro-Photoluminescence Mapping of Defect Structures in SiC Wafers

2007 ◽  
Vol 556-557 ◽  
pp. 383-386 ◽  
Author(s):  
John Hennessy ◽  
Tom Ryan
Keyword(s):  
Carrier Lifetime ◽  
Deep Level ◽  
Complex Function ◽  
Band Edge ◽  
Structural Defects ◽  
Band Edge Emission ◽  
Interfacial Defects ◽  
Pl Mapping ◽  
Boron Acceptor ◽  
Excitation Conditions

Micro-photoluminescence can be used to image electrically active structural defects in SiC. Under suitable excitation conditions it is possible to observe both band-edge PL and near bandedge PL from recombination via a shallow boron acceptor. The intensity of the band-edge emission is related to the carrier lifetime – and is reduced by the presence of structural or interfacial defects. The intensity of the deep level PL is a complex function of the number of radiative centers and the number of centers limiting carrier lifetime. Micro-PL mapping can provide information on the spatial distribution of electrically active defects in SiC.

Characterization of SiC Wafers by Photoluminescence Mapping

2006 ◽  
Vol 527-529 ◽  
pp. 711-716 ◽  
Author(s):  
Michio Tajima ◽  
E. Higashi ◽  
Toshihiko Hayashi ◽  
Hiroyuki Kinoshita ◽  
Hiromu Shiomi
Keyword(s):  
Room Temperature ◽  
Deep Level ◽  
Structural Defects ◽  
Near Band Edge ◽  
Band Edge Emission ◽  
Intensity Mapping ◽  
Area Of Interest ◽  
Mapping System ◽  
Pl Mapping

The effectiveness of room-temperature photoluminescence (PL) mapping was demonstrated for nondestructive detection of structural defects, such as dislocations, micropipes and stacking faults, in SiC wafers. PL spectra of bulk wafers were dominated by deep-level emissions due to Si vacancies, vanadium and undefined centers like UD-1 at room temperature, while those from epitaxial wafers involved near band-edge emission. We developed a whole-wafer PL intensity mapping system with a capability of zooming in on the area of interest with a spatial resolution as high as 1 μm, and showed that the mapping patterns agree well with the etch-pit patterns originating from the structural defects both on a wafer scale and on a microscopic scale. The intensity contrast around the defects varied depending on the emission band, suggesting differences in their interactions with impurities and point defects.

Spectroscopy Studies of InP Nanocrystals Synthesized Through a Fast Reaction

2003 ◽  
Vol 789 ◽  
Author(s):  
Madalina Furis ◽  
David J. MacRae ◽  
D. W. Lucey ◽  
Yudhisthira Sahoo ◽  
Alexander N. Cartwright ◽  
...  
Keyword(s):  
Deep Level ◽  
Surface States ◽  
Spectroscopic Characterization ◽  
Etching Process ◽  
Band Edge ◽  
Band Edge Emission ◽  
Fast Reaction ◽  
Surface Trap ◽  
Sharp Feature ◽  
Pl Spectrum

ABSTRACTWe present spectroscopic characterization of InP nanocrystals grown through a fast reaction in a non-coordinating solvent. The photoluminescence (PL) spectra collected from these nanocrystals exhibit a sharp feature associated with the band-edge emission and a broad infrared feature associated with deep level surface trap emission. The emission efficiencies of the as-grown nanocrystals vary between 0.3% and 1% from sample to sample. After undergoing an HF etching process, the emission efficiency increases to 18% and the emission associated with surface states is eliminated from the PL spectrum. Time-resolved photoluminescence (TRPL) experiments conducted at room temperature on the as-grown and HF-etched nanocrystals show that before etching the PL intensity decay is multi-exponential, with a fast (3ns) component independent of wavelength, associated with the non-radiative recombination processes. The etching process effectively eliminates the non-radiative component and the post-etching PL decay can be fitted with a single exponential decay characterized by long (45ns) lifetimes. We tentatively associate these long lifetimes with the recombination of carriers from spin-forbidden states. This assignment is supported by the observation of a significant redshift of the feature associated with band-edge recombination in the PL spectrum with respect to the lowest energy feature in the photoluminescence excitation (PLE) spectrum.

Cathodoluminescence, Photoluminescence, and Optical Absorbance Spectroscopy of Aluminum Gallium Nitride (AlxGa1−xN) Films

1998 ◽  
Vol 13 (9) ◽  
pp. 2480-2497 ◽  
Author(s):  
Lawrence H. Robins ◽  
Jeremiah R. Lowney ◽  
Dennis K. Wickenden
Keyword(s):  
Gallium Nitride ◽  
Aluminum Gallium Nitride ◽  
Deep Level ◽  
Chemical Vapor ◽  
Band Edge ◽  
Structural Defects ◽  
Excitation Mode ◽  
Optical Absorbance ◽  
Pl Spectra ◽  
Film Substrate

Aluminum gallium nitride (AlxGa1−xN) films, grown by metalorganic chemical vapor deposition on sapphire, were characterized by low-temperature cathodoluminescence (CL) and photoluminescence (PL), and room-temperature optical absorbance. The aluminum fractions are estimated to range from x = 0 to x = 0.444. Most films were silicon-doped. The absorption spectra have a Urbach (exponential) form below the bandgap. The width of the Urbach edge, EU, increases with Al fraction, x, as EU = (0.045 +1 0.104x) eV. The luminescence (CL or PL) spectra show a relatively narrow band-edge peak and a broad deep-level peak. The full-widths at half-maximum of the band-edge CL peaks (measured at T = 15 K) are remarkably similar to the Urbach absorption widths, EU (measured at T = 300 K). PL spectra were obtained from the top surfaces and the film-substrate interfaces of several films. The interface PL spectra of some films show an extra peak 0.15 eV to 0.45 eV below the bandgap, which is ascribed to structural defects or impurity phases localized near the interface. The energy of the band-edge luminescence peak shifts with excitation mode (CL, top-surface PL, or interface PL). This effect is attributed to the variation of the excitation depth, between the top surface and film-substrate interface, with excitation mode, together with the depth variation of film properties such as residual stress or aluminum fraction.

Influence of Epilayer Thickness and Structural Defects on the Minority Carrier Lifetime in 4H-SiC

2013 ◽  
Vol 740-742 ◽  
pp. 633-636 ◽  
Author(s):  
Birgit Kallinger ◽  
Patrick Berwian ◽  
Jochen Friedrich ◽  
Mathias Rommel ◽  
Maral Azizi ◽  
...  
Keyword(s):  
Carrier Lifetime ◽  
Minority Carrier ◽  
Deep Level ◽  
Surface Recombination ◽  
Minority Carrier Lifetime ◽  
Structural Defects ◽  
Effective Lifetime ◽  
Recombination Lifetime ◽  
Photoconductivity Decay ◽  
Transient Spectroscopy

4H-SiC homoepitaxial layers with different thicknesses from 12.5 µm up to 50 µm were investigated by microwave-detected photoconductivity decay (µ-PCD), deep level transient spectroscopy (DLTS) and defect selective etching (DSE) to shed light on the influence of the epilayer thickness and structural defects on the effective minority carrier lifetime. It is shown that the effective lifetime, resulting directly from the µ-PCD measurement, is significantly influenced by the surface recombination lifetime. Therefore, an adequate correction of the measured data is necessary to determine the bulk lifetime. The bulk lifetime of these epilayers is in the order of several microseconds. Furthermore, areas with high dislocation density are correlated to areas with locally reduced effective lifetime.

Long Charge Carrier Lifetime in As-Grown 4H-SiC Epilayer

2016 ◽  
Vol 858 ◽  
pp. 125-128
Author(s):  
Robin Karhu ◽  
Ian Booker ◽  
Ivan G. Ivanov ◽  
Erik Janzén ◽  
Jawad ul Hassan
Keyword(s):  
Carrier Lifetime ◽  
Deep Level ◽  
Optical Microscope ◽  
Structural Defects ◽  
Time Resolved ◽  
Microscope Images ◽  
Transient Spectroscopy ◽  
Time Resolved Photoluminescence ◽  
Koh Etching ◽  
Charge Carrier Lifetime

Over 150 μm thick epilayers of 4H-SiC with long carrier lifetime have been grown with a chlorinated growth process. The carrier lifetime have been determined by time resolved photoluminescence (TRPL), the lifetime varies a lot between different areas of the sample. This study investigates the origins of lifetime variations in different regions using deep level transient spectroscopy (DLTS), low temperature photoluminescence (LTPL) and a combination of KOH etching and optical microscopy. From optical microscope images it is shown that the area with the shortest carrier lifetime corresponds to an area with high density of structural defects.

Characterization of GaN Films on Sapphire by Cathodoluminescence

1996 ◽  
Vol 449 ◽  
Author(s):  
L.-L. Chao ◽  
G. S. Cargill ◽  
C. Kothandaraman
Keyword(s):  
Deep Level ◽  
Luminescent Properties ◽  
Deep Level Emission ◽  
Band Edge ◽  
Near Band Edge Emission ◽  
Near Band Edge ◽  
Band Edge Emission ◽  
Edge Emission ◽  
Luminescence Efficiency ◽  
Si Doped

ABSTRACTCathodoluminescence (CL) spectroscopy and microscopy were used to study the luminescent properties of a variety of GaN films, both Si-doped and unintentionally-doped, grown on sapphire substrates. A narrow and intense near band-edge emission was found in the CL spectrum of each film examined, and deep-level emission was also observed for some of the films. The luminescence efficiency of near band-edge emission increased with a faster rate than that of deep-level emission when the pumping current was increased. Spatial nonuniformities of luminescence were observed in monochromatic CL microscopy, and microstructures were observed in scanning electron microscopy. No correlations between luminescence features and microstructural features were seen. Degradation of near band-edge luminescence was observed, accompanied by growth of deep-level emission.

Ultrafast Carrier Dynamics, Optical Amplification, and Lasing in Nanocrystal Quantum Dots

MRS Bulletin ◽  
2001 ◽  
Vol 26 (12) ◽  
pp. 998-1004 ◽  
Author(s):  
Victor I. Klimov ◽  
Moungi G. Bawendi
Keyword(s):  
Quantum Dots ◽  
Quantum Wells ◽  
Quantum Wires ◽  
Electronic States ◽  
Three Dimensions ◽  
Band Edge ◽  
Lasing Threshold ◽  
Wide Energy Range ◽  
Band Edge Emission ◽  
Edge States

Semiconductor materials are widely used in both optically and electrically pumped lasers. The use of semiconductor quantum wells (QWs) as optical-gain media has resulted in important advances in laser technology. QWs have a two-dimensional, step-like density of electronic states that is nonzero at the band edge, enabling a higher concentration of carriers to contribute to the band-edge emission and leading to a reduced lasing threshold, improved temperature stability, and a narrower emission line. A further enhancement in the density of the band-edge states and an associated reduction in the lasing threshold are in principle possible using quantum wires and quantum dots (QDs), in which the confinement is in two and three dimensions, respectively. In very small dots, the spacing of the electronic states is much greater than the available thermal energy (strong confinement), inhibiting thermal depopulation of the lowest electronic states. This effect should result in a lasing threshold that is temperatureinsensitive at an excitation level of only 1 electron-hole (e-h) pair per dot on average. Additionally, QDs in the strongconfinement regime have an emission wavelength that is a pronounced function of size, adding the advantage of continuous spectral tunability over a wide energy range simply by changing the size of the dots.

scholarly journals Origin of long lifetime of band-edge charge carriers in organic–inorganic lead iodide perovskites

2017 ◽  
Vol 114 (29) ◽  
pp. 7519-7524 ◽  
Author(s):  
Tianran Chen ◽  
Wei-Liang Chen ◽  
Benjamin J. Foley ◽  
Jooseop Lee ◽  
Jacob P. C. Ruff ◽  
...  
Keyword(s):  
High Performance ◽  
Carrier Lifetime ◽  
Charge Carriers ◽  
Band Edge ◽  
Lead Iodide ◽  
Solar Cell Performance ◽  
Photovoltaic Materials ◽  
Wide Range ◽  
Long Lifetime ◽  
Photon Recycling

Long carrier lifetime is what makes hybrid organic–inorganic perovskites high-performance photovoltaic materials. Several microscopic mechanisms behind the unusually long carrier lifetime have been proposed, such as formation of large polarons, Rashba effect, ferroelectric domains, and photon recycling. Here, we show that the screening of band-edge charge carriers by rotation of organic cation molecules can be a major contribution to the prolonged carrier lifetime. Our results reveal that the band-edge carrier lifetime increases when the system enters from a phase with lower rotational entropy to another phase with higher entropy. These results imply that the recombination of the photoexcited electrons and holes is suppressed by the screening, leading to the formation of polarons and thereby extending the lifetime. Thus, searching for organic–inorganic perovskites with high rotational entropy over a wide range of temperature may be a key to achieve superior solar cell performance.

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