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19 Aug 1991

Volume 59, Issue 8, pp. 885-996

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Picosecond optical nonlinearities in lead chalcogenide semiconductors

Robert Klann, Rainer Buhleier, Thomas Elsaesser, and Armin Lambrecht

Appl. Phys. Lett. 59, 885 (1991); http://dx.doi.org/10.1063/1.106381 (3 pages) | Cited 6 times

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Optical nonlinearities of PbSe are studied in picosecond pump‐probe experiments at wavelengths from 4 to 8 μm. Excitation of an electron‐hole plasma leads to a shift of the absorption edge to higher energies and to large changes of the refractive index by up to −0.1 for a carrier density of 4×1017 cm−3. The optical nonlinearities result from band filling by both electrons and holes. The time‐dependent absorption change shows a partial recovery within 100 ps, giving evidence of enhanced recombination rates. Theoretical calculations of the absorption change are in agreement with the experimental data.
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42.65.Pc Optical bistability, multistability, and switching, including local field effects
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Electroabsorptive modulators in InGaAs/AlGaAs

B. Pezeshki, S. M. Lord, and J. S. Harris

Appl. Phys. Lett. 59, 888 (1991); http://dx.doi.org/10.1063/1.105266 (3 pages) | Cited 23 times

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Theoretical and experimental work shows that electroabsorption improves and the quantum‐confined Stark effect becomes stronger in In0.2Ga0.8As/AlxGa1−xAs quantum wells as the aluminum concentration (x) is increased in the barriers. This improved electroabsorption was used in a reflection modulator that exhibited the largest reported reflectivity change of 77%.
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78.66.Fd III-V semiconductors
78.66.Hf II-VI semiconductors
78.20.Jq Electro-optical effects
42.79.Hp Optical processors, correlators, and modulators

Chemically pumped atomic iodine pulse laser

M. Endo, K. Shiroki, and T. Uchiyama

Appl. Phys. Lett. 59, 891 (1991); http://dx.doi.org/10.1063/1.105267 (2 pages) | Cited 2 times

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A pulsed iodine laser driven by a chemical oxygen generator was developed. The energy deposition on I(2P3/2) was made by a high‐pressure pulsed O2(a1Δg) generator. Although this scheme is the same as the conventional chemically pumped oxygen‐iodine laser (COIL), it is unique in that the pulsed laser was extracted by the high‐energy density pulsed pumping scheme. The pulse energy obtained was 1.34 J, the pulse width was 1.5 ms, and the peak power was 900 W. The specific energy was estimated to be 3.6 J/l.
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42.55.Ks Chemical lasers

Interferometric characterization of 160 fs far‐infrared light pulses

B. I. Greene, J. F. Federici, D. R. Dykaar, R. R. Jones, and P. H. Bucksbaum

Appl. Phys. Lett. 59, 893 (1991); http://dx.doi.org/10.1063/1.105268 (3 pages) | Cited 34 times

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We report the first interferometric characterization of freely propagating, subpicosecond, far‐infrared (FIR) light pulses. FIR light was generated via short pulse photoexcitation of a semi‐insulating InP wafer. The half width of the intensity interferogram was 230 fs. The FIR light contained frequency components from 3 to 150 cm−1.
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07.60.Ly Interferometers
78.66.Qn Polymers; organic compounds
78.20.Jq Electro-optical effects

Blue‐green surface‐emitting second‐harmonic generators on (111)B GaAs

D. Vakhshoori, R. J. Fischer, M. Hong, D. L. Sivco, G. J. Zydzik, G. N. S. Chu, and A. Y. Cho

Appl. Phys. Lett. 59, 896 (1991); http://dx.doi.org/10.1063/1.105269 (3 pages) | Cited 35 times

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Passive devices capable of generating coherent blue‐green light radiated in a surface emitting geometry is realized on (111)B GaAs substrates. This substrate orientation is required by the symmetry of the III–V crystals for the particular nonlinear counterpropagating interaction under consideration. The visible light output power versus the fundamental optical power is measured and shown to agree with the theory. This result demonstrates the feasibility of active visible surface emitting generators in the milliwatt output power range on (111)B substrate.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
85.60.Jb Light-emitting devices

Novel phased array optical scanning device implemented using GaAs/AlGaAs technology

D. R. Wight, J. M. Heaton, B. T. Hughes, J. C. H. Birbeck, K. P. Hilton, and D. J. Taylor

Appl. Phys. Lett. 59, 899 (1991); http://dx.doi.org/10.1063/1.105270 (3 pages) | Cited 13 times

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A novel type of optical beam scanning device based on the same principle as a phased array radar has been made and demonstrated. This phased array optical scanning device consisted of a uniformly illuminated array of ten closely spaced, single mode GaAs/AlGaAs electrooptic waveguides, each of which was individually addressed to give more than 2π radians of optical phase control. This gave a line of ten point sources of light on a 3 μm pitch at the output face of the array. By independently phase shifting these light sources the output wavefront was controlled to scan a 2° wide beam through 20° in the far field.
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85.60.-q Optoelectronic devices
42.79.Fm Reflectors, beam splitters, and deflectors
42.79.Ls Scanners, image intensifiers, and image converters
42.55.Mv Dye lasers
42.82.-m Integrated optics

Guest‐host polymer fibers for nonlinear optics

M. G. Kuzyk, U. C. Paek, and C. W. Dirk

Appl. Phys. Lett. 59, 902 (1991); http://dx.doi.org/10.1063/1.105271 (3 pages) | Cited 32 times

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We report on the fabrication of poly(methyl methacrylate) (PMMA) nonlinear optical fibers with dye‐doped cores. The dye‐doped cores have an elevated refractive index that defines a waveguiding region with a large third‐order susceptibility and with single‐mode dimensions. The measured third‐order susceptibility of a squarylium‐doped PMMA film material and the measured optical loss of the dye‐doped fiber core results in a figure of merit that is suitable for all‐optical device applications at λ=1.3 μm. The impact of further improvements in PMMA loss and chromophore nonlinearity are also discussed.
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42.81.Bm Fabrication, cladding, and splicing
42.81.Dp Propagation, scattering, and losses; solitons
42.70.-a Optical materials

Effects of nearest‐neighbor pairs on the energy transfer in Nd:YAG

V. Lupei, A. Lupei, S. Georgescu, and I. Ursu

Appl. Phys. Lett. 59, 905 (1991); http://dx.doi.org/10.1063/1.106420 (3 pages) | Cited 8 times

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An analysis of the luminescence quenching of 4F3/2 level of Nd3+ in YAG is presented in terms of two models: uniform random distribution and nonuniform placement of activators. It is shown that the correlated placement model for Nd3+ ions, assuming the absence, based on ionic size arguments, of Nd3+ ions in nearest‐neighbor sites, is in contradiction with high resolution absorption spectra as well as quantum yield data. The anomalous decay can be described by energy transfer theory for a uniform distribution with a short‐range interaction connecting the nearest‐neighbor pairs and with dipolar interaction inside the other donor‐acceptor pairs.  
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42.55.Rz Doped-insulator lasers and other solid state lasers
78.55.Hx Other solid inorganic materials

Nonlinear resolution improvement and second‐harmonic generation of a pressurized superfluid 4He acoustic microscope

Koichi Karaki, Takehiko Saito, Koichi Matsumoto, and Yuichi Okuda

Appl. Phys. Lett. 59, 908 (1991); http://dx.doi.org/10.1063/1.106297 (3 pages) | Cited 3 times

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We observed the input power dependence of the second‐harmonic generation of a 370‐MHz focused acoustic beam in pressurized superfluid 4He at about 300 mK. We also measured the resolving power of a reflection mode acoustic microscope using pressurized superfluid 4He as a coupling liquid under 11 atm (anomalous dispersion region) and 21 atm (normal dispersion region). At the nonlinear power region of each pressure, the resolution was improved beyond the diffraction limit. Results of these two experiments confirmed that the higher harmonics are generated and they are converted to the fundamental as the wave propagates through the focal point. The higher harmonics play an important role in recently observed exotic nonlinear phenomenon in pressurized superfluid 4He.
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67.25.dt Sound and excitations
43.35.-c Ultrasonics, quantum acoustics, and physical effects of sound
43.25.-x Nonlinear acoustics

Microcrystalline diamond deposition using a combustion flame of acetylene and oxygen with a magnetic field

Toshimi Abe, Maki Suemitsu, Nobuo Miyamoto, and Noriyoshi Sato

Appl. Phys. Lett. 59, 911 (1991); http://dx.doi.org/10.1063/1.106298 (3 pages) | Cited 11 times

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Microcrystalline diamonds were successfully deposited on an abraded molybdenum surface under a magnetic field using a combustion flame of acetylene (C2H2) and oxygen (O2) gases. The deposition rate was about 1 μm/min, which is an order larger than that obtained by conventional chemical‐vapor‐deposition methods. The magnetic field led to an increase of the deposited area and of the microcrystal diameter. The microcrystals show good crystallinity as observed from scanning electron microscopy, reflective electron diffraction, and x‐ray diffraction measurements.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
07.79.Cz Scanning tunneling microscopes
61.05.-a Techniques for structure determination
61.05.cf X-ray scattering (including small-angle scattering)
61.05.cj X-ray absorption spectroscopy: EXAFS, NEXAFS, XANES, etc.

Reactive ion etching of copper in SiCl4‐based plasmas

B. J. Howard and Ch. Steinbrüchel

Appl. Phys. Lett. 59, 914 (1991); http://dx.doi.org/10.1063/1.106299 (3 pages) | Cited 26 times

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Copper may become an alternative to aluminum as an interconnect material in ultralarge scale integration multilevel metallization schemes if it is possible to pattern Cu by dry etching in a manufacturable process. Here we report results on the reactive ion etching of Cu in SiCl4/Ar and SiCl4/N2 plasmas. Etching has been investigated as a function of gas composition, pressure, and substrate temperature. We have obtained etch rates as high as 850 Å/min using SiCl4/N2 and a substrate temperature of ∼ 220 °C, with excellent etch selectivity of Cu relative to polyimide and SiO2. We demonstrate that it is feasible to pattern Cu anisotropically using polyimide as a high‐temperature etch mask.
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81.05.Bx Metals, semimetals, and alloys
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Freely suspended liquid crystal film transfer: A new method of creating thin smectic films on solid substrates

Joseph Maclennan, Gero Decher, and Ulrich Sohling

Appl. Phys. Lett. 59, 917 (1991); http://dx.doi.org/10.1063/1.106300 (3 pages) | Cited 11 times

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A novel method of creating ultrathin, well‐ordered organic multilayer films is described, in which freely suspended smectic liquid crystal films are transferred to solid substrates. X‐ray and optical measurements show that both the smectic layering and the in‐plane director field, which are the defining characteristic structures of the original free film, are maintained after transfer. This method, in contrast to traditional techniques of organic film deposition, offers the possibility of orienting the initial freely suspended liquid crystal films using applied fields to obtain highly organized monodomain structures after transfer.
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61.30.Eb Experimental determinations of smectic, nematic, cholesteric, and other structures
61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
68.15.+e Liquid thin films
68.08.-p Liquid-solid interfaces
68.43.-h Chemisorption/physisorption: adsorbates on surfaces

Work hardening and strain relaxation in strained‐layer buffers

J. R. Willis, S. C. Jain, and R. Bullough

Appl. Phys. Lett. 59, 920 (1991); http://dx.doi.org/10.1063/1.106301 (3 pages) | Cited 20 times

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The driving force for the introduction of dislocations at the interface between a strained buffer layer and its substrate is considered. An exact assessment is made of the difference in energy between a system in which prestrain is partially relaxed by the presence of a periodic array of dislocations between layer and substrate and one containing a periodic array which is complete except for one vacant site. The difference provides an expression for the driving force, for introducing the ‘‘last’’ dislocation to complete the periodic array, by the motion of a threading dislocation. All of the dislocation stress fields are accounted for exactly. It emerges that, contrary to intuition, the fluctuating part of the dislocation stress field contributes a term which is attractive rather than repulsive, which is the opposite effect to that found in ‘‘Taylor hardening.’’
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61.72.Lk Linear defects: dislocations, disclinations
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.40.-z Treatment of materials and its effects on microstructure, nanostructure, and properties

Photoluminescence and secondary‐ion mass spectrometry studies of rapid‐thermal‐annealed silicon coimplanted with phosphorus in GaAs

G. Marrakchi, A. Laugier, G. Guillot, S. Alaya, and H. Maaref

Appl. Phys. Lett. 59, 923 (1991); http://dx.doi.org/10.1063/1.106302 (3 pages) | Cited 2 times

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Coimplantation effects of phosphorus (P) are studied for Si‐implanted GaAs by photoluminescence and secondary‐ion mass spectrometry. P coimplantation decreases SiAs acceptor intensity. At high temperatures rapid thermal annealing causes As loss, which favors the formation of the SiAs‐VAs complex. Diffusion of Si towards the GaAs bulk is not caused by P coimplantation but rather by the presence of carbon.
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72.80.Ey III-V and II-VI semiconductors
81.65.-b Surface treatments
78.55.Cr III-V semiconductors
71.55.Eq III-V semiconductors

Ultrashort carrier lifetimes in H+ bombarded InP

K. F. Lamprecht, S. Juen, L. Palmetshofer, and R. A. Höpfel

Appl. Phys. Lett. 59, 926 (1991); http://dx.doi.org/10.1063/1.106303 (3 pages) | Cited 19 times

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We studied the lifetimes of photoexcited carriers in H+ bombarded InP for different damage doses by means of femtosecond luminescence spectroscopy. The lifetime decreases down to 95 fs for a dose of 1×1016 cm−2. To our knowledge this is the shortest decay time for spontaneous light emission ever observed. The luminescence spectrum of the most damaged sample is inverted, indicating nonthermalized carrier distributions.
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78.55.Cr III-V semiconductors
78.47.-p Spectroscopy of solid state dynamics
61.80.Jh Ion radiation effects

New method to suppress encroachment by plasma‐deposited β‐phase tungsten nitride thin films

Yong Tae Kim and Suk‐Ki Min

Appl. Phys. Lett. 59, 929 (1991); http://dx.doi.org/10.1063/1.106304 (3 pages) | Cited 14 times

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<m1;40p>Tungsten nitride thin films are prepared with the WF6‐NH3‐H2 system by the plasma‐enhanced chemical vapor deposition method. X‐ray diffraction and Auger spectroscopy show that the crystal structure and the composition of tungsten nitride thin films grown at the WF6/NH3 ratio of 1 are β‐phase W2N. The resistivity of W2N is about 190–210 μΩ cm and it is demonstrated that severe encroachment and SiO2 etching during the low‐pressure chemical vapor deposition of tungsten is remarkably suppressed by the predeposition of W2N.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
85.40.Ls Metallization, contacts, interconnects; device isolation
73.61.At Metal and metallic alloys

Undoped semi‐insulating InP by high‐pressure annealing

K. Kainosho, H. Shimakura, H. Yamamoto, and O. Oda

Appl. Phys. Lett. 59, 932 (1991); http://dx.doi.org/10.1063/1.106305 (3 pages) | Cited 35 times

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Undoped semi‐insulating (SI) InP wafers were obtained by high‐temperature annealing under high phosphorus over pressure. These wafers show resistivities higher than 107 Ω cm, with mobilities greater than 4000 cm2 V−1 s−1. The SI properties could be held even after cap annealing with SiNx films at 700 °C for 15 min. The activation energy of deep levels causing the semi‐insulation was estimated as 0.64 eV. Photoluminescence measurements made on undoped SI InP show hitherto unknown peaks in the long wavelength region between 1000 and 1400 nm.
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72.80.Ey III-V and II-VI semiconductors
61.72.Bb Theories and models of crystal defects
78.55.Cr III-V semiconductors
71.55.Eq III-V semiconductors

Laser ablation of aluminum at 193, 248, and 351 nm

Hongxin Wang, A. P. Salzberg, and Brad R. Weiner

Appl. Phys. Lett. 59, 935 (1991); http://dx.doi.org/10.1063/1.106306 (3 pages) | Cited 41 times

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Pulsed laser ablation of an aluminum target at 193, 248, and 351 nm has been investigated by laser‐induced fluorescence (LIF) spectroscopy. Velocity distributions of the ablated Al atoms have been measured directly by monitoring their flight times from the target to the probe laser beam, and by Doppler laser spectroscopy. The velocity distributions resulting from the three wavelengths can all be characterized as hyperthermal, with average velocities of between 4.5×105 and 6.5×105 cm/s over a fluence range of 0.3–6.5 J/cm2. Average values of the Al atom distribution can also be derived by measuring the AlO internal energy distribution of the ‘‘hot’’ Al atom reaction with low pressures of O2. For excimer laser ablation of aluminum at 248 nm, we have found an average Al atom velocity of ≳2×105 cm/s. Possible mechanisms for the production of these hyperthermal velocity distributions are discussed.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
79.20.Ds Laser-beam impact phenomena
07.77.-n Atomic, molecular, and charged-particle sources and detectors
37.20.+j Atomic and molecular beam sources and techniques
32.50.+d Fluorescence, phosphorescence (including quenching)

Indium‐Hg vacancy interactions in Hg1−xCdxTe measured by perturbed angular correlation

W. C. Hughes, M. L. Swanson, and J. C. Austin

Appl. Phys. Lett. 59, 938 (1991); http://dx.doi.org/10.1063/1.106307 (3 pages) | Cited 6 times

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The interaction of mercury vacancies with dopant indium atoms in Hg0.79Cd0.21Te was studied using the perturbed γγ angular correlation (PAC) technique. Two dominant PAC signals, characterized by quadrupole interaction strengths νQ1=83 MHz and νQ2= 91 MHz and asymmetry parameters η1=η2=0.08, were observed and attributed to one or more In‐VHg complexes. The complexes appeared after annealing doped samples at T≥350 °C in vacuum and quenching. The fraction of In atoms associated with vacancies was increased further by annealing at 80 °C for ≳10 h. The In‐vacancy complexes vanished on annealing in a Hg‐saturated atmosphere.
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61.72.Yx Interaction between different crystal defects; gettering effect
61.72.U- Doping and impurity implantation
76.80.+y Mössbauer effect; other γ-ray spectroscopy
61.72.jd Vacancies
61.72.jj Interstitials

Defects in organometallic vapor‐phase epitaxy‐grown GaInP layers

S. L. Feng, J. C. Bourgoin, F. Omnes, and M. Razeghi

Appl. Phys. Lett. 59, 941 (1991); http://dx.doi.org/10.1063/1.106308 (3 pages) | Cited 19 times

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Nonintentionally doped metalorganic vapor‐phase epitaxy Ga1−x InxP layers, having an alloy composition (x = 0.49) corresponding to a lattice matched to GaAs, grown by metalorganic chemical vapor deposition, have been studied by capacitance‐voltage and deep‐ level transient spectroscopy techniques. They are found to exhibit a free‐carrier concentration at room temperature of the order of 1015 cm−3. Two electron traps have been detected. The first one, at 75 meV below the conduction band, is in small concentration (∼ 1013 cm−3) while the other, at about 0.9 eV and emitting electrons above room temperature, has a concentration in the range 1014–1015 cm−3.
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61.72.J- Point defects and defect clusters
71.55.Eq III-V semiconductors
73.61.Ey III-V semiconductors
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Epitaxial growth of zinc blende and wurtzitic gallium nitride thin films on (001) silicon

T. Lei, M. Fanciulli, R. J. Molnar, T. D. Moustakas, R. J. Graham, and J. Scanlon

Appl. Phys. Lett. 59, 944 (1991); http://dx.doi.org/10.1063/1.106309 (3 pages) | Cited 162 times

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Zinc blende and wurtzitic GaN films have been epitaxially grown onto (001)Si by electron <m1;&1p>cyclotron resonance microwave plasma‐assisted molecular beam epitaxy, using a two‐step growth process. In this process a thin buffer layer is grown at relatively low temperatures followed by a higher temperature growth of the rest of the film. GaN films grown on a single crystalline GaN buffer have the zinc blende structure, while those grown on a polycrystalline or amorphous buffer have the wurtzitic structure.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.-a Thin film structure and morphology
61.05.jh Low-energy electron diffraction (LEED) and reflection high-energy electron diffraction (RHEED)

Mechanism of forming ohmic contacts to GaAs

Paul H. Holloway, Liu Lu‐Min Yeh, David H. Powell, and Alan Brown

Appl. Phys. Lett. 59, 947 (1991); http://dx.doi.org/10.1063/1.106310 (3 pages) | Cited 11 times

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The distribution of Si dopant at the Au/GaAs interface after heat treatment has been studied using spatially resolved secondary‐ion mass spectrometry. Previously it has been shown that heat treatment changes as deposited Au thin film from Schottky contacts to ohmic contacts. The present study shows that the transition to an ohmic contact results from segregation of dopants in areas where GaAs is decomposed by reacting with the Au overlayer. Thus the ohmic contact is spatially very inhomogeneous at the metal/semiconductor interface. The mechanism leading to concentrations of the Si and nonuniform ohmic contacts is discussed, and segregation to the solid during decomposition of the GaAs is the most likely mechanism.
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73.40.Cg Contact resistance, contact potential
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
85.30.Hi Surface barrier, boundary, and point contact devices

In situ study of the growth of hydrogenated amorphous silicon by infrared ellipsometry

N. Blayo and B. Drévillon

Appl. Phys. Lett. 59, 950 (1991); http://dx.doi.org/10.1063/1.106311 (3 pages) | Cited 19 times

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The early stage of the growth of plasma deposited amorphous silicon (a‐Si:H) on glass substrates is investigated by in situ infrared phase modulated ellipsometry in the silicon–hydrogen stretching mode region. Analysis of the spectra provides unprecedented sensitivity and quantitative information on the film evolution. In particular SiH, SiH2, and SiH3 bonds are identified in 5–20 Å thick samples. The bond densities of SiH and SiH2 in thin films are estimated. After the interaction with the substrate, a‐Si:H films grow beneath a hydrogen rich overlayer containing SiH2 and SiH3 bonds. At 250 °C the thickness of this overlayer is compatible with one monolayer. The hydrogen‐passivated surface of a‐Si:H is then weakly reactive.
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68.55.-a Thin film structure and morphology
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
72.80.Ng Disordered solids
07.60.Fs Polarimeters and ellipsometers

Epitaxial growth of α‐Fe films on Si(111) substrates

Yang‐Tse Cheng, Yen‐Lung Chen, M. M. Karmarkar, and Wen‐Jin Meng

Appl. Phys. Lett. 59, 953 (1991); http://dx.doi.org/10.1063/1.106312 (3 pages) | Cited 25 times

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Epitaxial α‐Fe films have been grown on HF cleaned Si(111) substrates at 30 °C by electron beam evaporation in an ultrahigh vacuum environment to a thickness of several thousands of Angstroms. Conventional θ−2θ x‐ray diffraction shows that only the Fe(222) peak is present, indicating that the films are oriented with the Fe(111) plane parallel to the Si(111) plane. Transmission electron microscopy shows that the Fe[110] direction is parallel to the Si[110] direction in the plane of the substrate.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.55.-a Thin film structure and morphology

Observation of enhanced infrared photoresponse in forward‐biased amorphous silicon p‐i‐n diodes

J. Wind and G. Müller

Appl. Phys. Lett. 59, 956 (1991); http://dx.doi.org/10.1063/1.106313 (2 pages) | Cited 5 times

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The photoconductive response of hydrogenated amorphous silicon (a‐Si:H) p‐i‐n diodes has been investigated under conditions of low‐temperature operation. We show that cooled p‐i‐n diodes exhibit an enhanced infrared response when operated under forward bias conditions. The induced IR response is of the order of 10−3A/W, extending out to wavelengths of about 2–3 μm with the long wavelength cutoff being determined by the properties of the glass/indium–tin–oxide entrance window. We propose that the IR photoeffect is due to the re‐excitation of band‐tail trapped excess carriers injected into the localized conduction and valence band tail states in the vicinity of the n+‐ and p+‐contact regions.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
72.40.+w Photoconduction and photovoltaic effects
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