Recombination at surface states in GaN

2001 ◽  
Vol 680 ◽  
Author(s):  
M. A. Reshchikov ◽  
P. Visconti ◽  
K. M. Jones ◽  
H. Morkoç ◽  
C. W. Litton ◽  
...  
Keyword(s):  
Surface States ◽  
Depletion Region ◽  
Nonradiative Recombination ◽  
Etch Pits ◽  
Blue Band ◽  
Near Surface ◽  
Force Microscopy ◽  
Uv Illumination ◽  
Photogenerated Electrons ◽  
Subsequent Exposure

ABSTRACTWe have studied radiative and nonradiative recombination at surface states in GaN, including as-grown samples and those treated with acids or bases. The surface states manifested themselves in two ways: (i) a reversible increase of the photoluminescence (PL) intensity after ultraviolet (UV) illumination in vacuum and (ii) appearance of new PL bands after treatment with acid or base and subsequent exposure to air. It has been established that the GaN surface physi-sorbs species from air (presumably oxygen) which induce surface states acting as nonradiative recombination centers. It has been found that nonradiative recombination of photogenerated carriers via surface states comprises more than 70% of the recombination in some GaN samples. Another type of the surface state, which participates in radiative recombination, has been found in GaN samples with Ga polarity after brief etching of the surface with hot acid or base and subsequent exposure to air. In such samples, a broad PL band emerges in the blue region of the spectrum at low temperatures. The blue band has been attributed to transitions of photogenerated electrons from donors in the near-surface depletion region to the surface states introduced by the above-mentioned procedure. The changes in the GaN surface caused by etching were examined by atomic force microscopy. In some samples the blue band appeared even when no evidence of the layer etching was found except for quite shallow etch pits formed at dislocation sites. The emerging blue band can be related to the surface states formed on the a-planes of etch pits.

Excitons bound to surface defects in GaN

2002 ◽  
Vol 743 ◽  
Author(s):  
M. A. Reshchikov ◽  
D. Huang ◽  
H. Morkoç
Keyword(s):  
Low Temperature ◽  
Surface Defects ◽  
Acceptor Pair ◽  
Force Microscopy ◽  
Uv Illumination ◽  
Atomic Force ◽  
Subsequent Exposure ◽  
Donor Acceptor ◽  
And Inversion ◽  
Microscopy Images

ABSTRACTSharp intense peaks are sometimes detected in the low-temperature photoluminescence (PL) spectrum of undoped GaN samples in the photon energy range of 3.0 – 3.46 eV. Some of these peaks can be attributed to excitons bound to dislocations and inversion domains, whereas some others originate from the GaN surface because they can be affected essentially by surface treatment. In our samples, grown by molecular beam epitaxy on sapphire substrate, the 3.42 eV peak always disappeared after removing the surface layer by etching for a few seconds in hot phosphoric acid. Atomic force microscopy images confirmed that such light etching modifies the surface morphology, although the etched depth is negligibly small. Moreover, intensities of two other peaks (at 3.32 and 3.35 eV) were observed to depend on sample etching, as well as on the length of subsequent exposure to air. The 3.32 and 3.35 eV peaks evolved with time of UV illumination, increasing by several times and demonstrating memory effect at low temperature. We attribute the 3.42 and 3.35 eV peaks to bound excitons, whereas the 3.32 eV peak is tentatively attributed to a surface donor-acceptor pair transition.

The Early Stages of Mimetite Dissolution in EDTA Studied with Atomic Force Microscopy and Scanning Electron Microscopy

2019 ◽  
Vol 25 (3) ◽  
pp. 810-816
Author(s):  
Tomasz Bajda ◽  
Maciej Manecki ◽  
Marek Matyjasik
Keyword(s):  
Electron Microscopy ◽  
Scanning Electron Microscopy ◽  
Atomic Force Microscopy ◽  
Contaminated Soils ◽  
Acetic Acid Solution ◽  
Etch Pits ◽  
Near Surface ◽  
Force Microscopy ◽  
Atomic Force ◽  
Scanning Electron

AbstractA mineral, mimetite Pb5(AsO4)3Cl, is one of the most insoluble minerals and continues to be considered a viable remedial strategy for immobilization of Pb and As from contaminated soils. It has been recognized that many well-known, naturally-occurring, and synthetic chelators strongly influence dissolution processes in near-surface geological environments. In this study, crystals of mimetite were observed in scanning electron microscopy (SEM) and atomic force microscopy (AFM) before and after dissolution in EDTA (ethylene diamine tetra-acetic acid) solution. Direct in situ observations at room temperature made in an AFM fluid cell revealed that the grain surface roughness has increased due to development of etch pits. Both hexagonal and prismatic walls developed dissolution features between 0.6 and 1.2 µm, respectively, during duration of the experiment. AFM observations suggest surface-controlled dissolution dominated step retrieval on both prismatic and hexagonal surfaces. SEM observations showed the development of rounded edges on hexagonal walls and elongated, oval etch pits on the prismatic wall. These results, representing early dissolution patterns on mimetite surfaces, might suggest that low pH conditions in soils containing organic acids similar to EDTA might contribute to remobilization of Pb and As from mimetite when applied to stabilization of these toxic metals in contaminated soils.

Investigation of Surface Passivation in InAs/GaSb Strained-Layer-Superlattices Using Picosecond Excitation Correlation Measurement and Variable-Area Diode Array Surface Recombination Velocity Measurement

2005 ◽  
Vol 891 ◽  
Author(s):  
Zhimei Zhu ◽  
Elena Plis ◽  
Abdenour Amtout ◽  
Pallab Bhattacharya ◽  
Sanjay Krishna
Keyword(s):  
Infrared Detectors ◽  
Surface Passivation ◽  
Surface Recombination ◽  
Surface States ◽  
Depletion Region ◽  
Surface Recombination Velocity ◽  
Diode Array ◽  
Ammonium Sulfide ◽  
Picosecond Excitation ◽  
Recombination Velocity

ABSTRACTThe effect of ammonium sulfide passivation on InAs/GaSb superlattice infrared detectors was investigated using two complementary techniques, namely, picosecond excitation correlation (PEC) measurement and variable-area diode array (VADA) surface recombination velocity (SRV) measurement. PEC measurements were conducted on etched InAs/GaSb superlattice mesas, which were passivated in aqueous ammonium sulfide solutions of various strengths for several durations. The PEC signal's decay time constant (DTC) is proportional to carrier lifetimes. At 77 K the PEC signal's DTC of the as-grown InAs/GaSb superlattice sample was 2.0 ns, while that of the unpassivated etched sample was reduced to 1.2 ns by the surface states at the mesa sidewalls. The most effective ammonium sulfide passivation process increased the PEC signal's DTC to 10.4 ns. However it is difficult to isolate surface recombination from other processes that contribute to the lifetime using the PEC data, therefore a VADA SRV measurement was undertaken to determine the effect of passivation on surface recombination. The obtained SRV in the depletion region of the InAs/GaSb superlattice and GaSb junction was 1.1×106 cm/s for the unpassivated sample and 4.6×105 cm/s for the passivated sample. At 77 K the highest R0A value measured in our passivated devices was 2540 W cm2 versus 0.22 W cm2 for the unpassivated diodes. The results of the lifetime, the SRV and the R0A measurements indicate that ammonium sulfide passivation will improve the performance of InAs/GaSb superlattice infrared detectors.

scholarly journals Coincident Electron Channeling and Cathodoluminescence Studies of Threading Dislocations in GaN

2013 ◽  
Vol 20 (1) ◽  
pp. 55-60 ◽  
Author(s):  
Gunasekar Naresh-Kumar ◽  
Jochen Bruckbauer ◽  
Paul R. Edwards ◽  
Simon Kraeusel ◽  
Ben Hourahine ◽  
...  
Keyword(s):  
Structural Damage ◽  
Light Emission ◽  
Threading Dislocations ◽  
Nonradiative Recombination ◽  
Contrast Imaging ◽  
Force Microscopy ◽  
Electron Channeling ◽  
Microscopy Techniques ◽  
Cathodoluminescence Imaging ◽  
Edge Dislocations

AbstractWe combine two scanning electron microscopy techniques to investigate the influence of dislocations on the light emission from nitride semiconductors. Combining electron channeling contrast imaging and cathodoluminescence imaging enables both the structural and luminescence properties of a sample to be investigated without structural damage to the sample. The electron channeling contrast image is very sensitive to distortions of the crystal lattice, resulting in individual threading dislocations appearing as spots with black–white contrast. Dislocations giving rise to nonradiative recombination are observed as black spots in the cathodoluminescence image. Comparison of the images from exactly the same micron-scale region of a sample demonstrates a one-to-one correlation between the presence of single threading dislocations and resolved dark spots in the cathodoluminescence image. In addition, we have also obtained an atomic force microscopy image from the same region of the sample, which confirms that both pure edge dislocations and those with a screw component (i.e., screw and mixed dislocations) act as nonradiative recombination centers for the Si-doped c-plane GaN thin film investigated.

Theory of shallow donor impurity near-surface states in Si and Ge

1973 ◽  
Vol 34 (1) ◽  
pp. 108-118 ◽  
Author(s):  
Vidal Emmanuel Godwin ◽  
Wayne E. Tefft
Keyword(s):  
Surface States ◽  
Shallow Donor ◽  
Donor Impurity ◽  
Near Surface

scholarly journals Структура и механизмы образования наноразмерных пленок примесного металла кобальта и никеля в монокристаллах LiF и MgF-=SUB=-2-=/SUB=-

2021 ◽  
Vol 63 (9) ◽  
pp. 1340
Author(s):  
Н.А. Иванов ◽  
С.А. Небогин ◽  
С.С. Колесников ◽  
Л.И. Брюквина
Keyword(s):  
Electron Microscopy ◽  
Scanning Electron Microscopy ◽  
Etch Pits ◽  
Force Microscopy ◽  
Thermal Etching ◽  
Air Atmosphere ◽  
Atomic Force ◽  
Residual Air ◽  
Scanning Electron ◽  
Cobalt And Nickel

It is investigated the thermal etching of LiF and MgF2 crystals with cobalt and nickel impurities by means of scanning electron microscopy and atomic force microscopy with using decorating. It is shown that impurity inclusions leave the crystal from dislocations. The differences between of thermal etching in vacuum and air atmosphere take place. The crystallographic oriented terraced etch pits are formed after exit of impurities from dislocations. The square thermal etch pits are formed after thermal etching at 750°C in air. The surface impurity nanoscale film is formed at thermal etching. The oxidation of surface impurities observed at thermal etching in air atmosphere or in residual air atmosphere.

Atomic Force Microscopy of Atomic-Scale Ledges and Etch Pits Formed During Dissolution of Quartz

Science ◽  
1991 ◽  
Vol 251 (4999) ◽  
pp. 1343-1346 ◽  
Author(s):  
A. J. GRATZ ◽  
S. MANNE ◽  
P. K. HANSMA
Keyword(s):  
Atomic Force Microscopy ◽  
Atomic Scale ◽  
Etch Pits ◽  
Force Microscopy ◽  
Atomic Force

Influence of surface passivation on electric properties of individual GaAs nanowires studied by current–voltage AFM measurements

2016 ◽  
Vol 56 (2) ◽  
Author(s):  
Pavel Geydt ◽  
Prokhor A. Alekseev ◽  
Mikhail S. Dunaevskiy ◽  
Tuomas Haggrén ◽  
Joona-Pekko Kakko ◽  
...  
Keyword(s):  
Vertical Structure ◽  
Surface Passivation ◽  
Surface States ◽  
Electric Properties ◽  
Conductive Atomic Force Microscopy ◽  
Force Microscopy ◽  
Atomic Force ◽  
Gaas Nanowires ◽  
Current Voltage

Current–voltage (I–V) characteristics of vertical p-GaAs nanowires (NWs) covered by different surface passivation materials were experimentally measured by conductive atomic force microscopy (C-AFM). The obtained I–V curves for individual NWs with a diameter of 100 nm covered with AlGaAs, GaN, GaP or InP shell layers were compared to analyse the influence of surface passivation on the density of surface states and choose the most beneficial passivating material for technological applications. We have found the absence of a Schottky barrier between the golden catalytic cap on the top of a NW and the nanowire situated below and covered with an ultrathin GaP passivating layer. It was suggested that passivating material can arrange the heterostructure configuration with the GaAs NW near the Au cap. The latter mechanism was proposed to explain a strong energy barrier found in nanowires covered with InP passivation. AlGaAs passivation affected the forward threshold voltage of nanowires for NWs, which was measured simultaneously with the resistivity of each individual vertical structure from an array by means of AFM in the regime of measuring the I–V curves and onefold calculations. We made an attempt to develop the methodology of measurement and characterization of electric properties of passivated NWs.

Sign in / Sign up

Export Citation Format

Share Document