Abstract:Deep level defects in epitaxially grown high-conductivity zinc selenide were investigated using transient capacitance spectroscopy. A total of seven electron traps was observed in Au/ZnSe Schottky diodes and ZnSe/GaAs n-p heterojunctions, having activation energies of 0.24, 0.33, 0.35, 0.42, 0.54, 0.71, and 0.86 eV, respectively. The emission rate, capture cross-section prefactor, and concentration of each trap are reported in this paper. Trap concentrations ranged from 1011 to 1014 cm−3 depending upon the epi… Show more
“…eV, the donor level is approximately 0.15 eV below the conduction band edge, which agrees well with Iida, 49 Besomi, 50 and Meneses 47 who attributed the donor to a metal impurity, possibly indium. For the green emission, the…”
Section: Nano Letterssupporting
confidence: 87%
“…For the red emission, it is well-documented that the acceptor level exists eV above the valence band edge. − From eV, the donor level is approximately 0.15 eV below the conduction band edge, which agrees well with Iida, Besomi, and Meneses who attributed the donor to a metal impurity, possibly indium. For the green emission, the acceptor level ,, is approximately eV above the valence band edge, giving a donor energy level 0.03 eV below the conduction band edge, which is within the error of the shallow donor value given by the hydrogen model, meV.…”
Characterizing
point defects that produce deep states in nanostructures
is imperative when designing next-generation electronic and optoelectronic
devices. Light emission and carrier transport properties are strongly
influenced by the energy position and concentration of such states.
The primary objective of this work is to fingerprint the electronic
structure by characterizing the deep levels using a combined optical
and electronic characterization, considering ZnSe nanowires as an
example. Specifically, we use low temperature photoluminescence spectroscopy
to identify the dominant recombination mechanisms and determine the
total defect concentration. The carrier concentration and mobility
are then calculated from electron transport measurements using single
nanowire field effect transistors, and the measured experimental data
were used to construct a model describing the types, energies, and
ionized fraction of defects and calculate the deviation from stoichiometry.
This metrology is hence demonstrated to provide an unambiguous means
to determine a material’s electronic structure.
“…eV, the donor level is approximately 0.15 eV below the conduction band edge, which agrees well with Iida, 49 Besomi, 50 and Meneses 47 who attributed the donor to a metal impurity, possibly indium. For the green emission, the…”
Section: Nano Letterssupporting
confidence: 87%
“…For the red emission, it is well-documented that the acceptor level exists eV above the valence band edge. − From eV, the donor level is approximately 0.15 eV below the conduction band edge, which agrees well with Iida, Besomi, and Meneses who attributed the donor to a metal impurity, possibly indium. For the green emission, the acceptor level ,, is approximately eV above the valence band edge, giving a donor energy level 0.03 eV below the conduction band edge, which is within the error of the shallow donor value given by the hydrogen model, meV.…”
Characterizing
point defects that produce deep states in nanostructures
is imperative when designing next-generation electronic and optoelectronic
devices. Light emission and carrier transport properties are strongly
influenced by the energy position and concentration of such states.
The primary objective of this work is to fingerprint the electronic
structure by characterizing the deep levels using a combined optical
and electronic characterization, considering ZnSe nanowires as an
example. Specifically, we use low temperature photoluminescence spectroscopy
to identify the dominant recombination mechanisms and determine the
total defect concentration. The carrier concentration and mobility
are then calculated from electron transport measurements using single
nanowire field effect transistors, and the measured experimental data
were used to construct a model describing the types, energies, and
ionized fraction of defects and calculate the deviation from stoichiometry.
This metrology is hence demonstrated to provide an unambiguous means
to determine a material’s electronic structure.
“…In the as-grown array of nanowires, the measured k DL values show that the emission was dominated by DAP recombination. It is well known [17,18] that the red emission involves zinc vacancies, V Zn , and zinc interstitials, Zn i , and has a donor level, E d R , located 0.15 eV below the conduction band edge [21,37,38]. Meanwhile, the green emission involves V Zn and substitutional impurities residing on a zinc lattice site, and is sometimes called the A-center [39].…”
Wide-gap semiconductors are excellent candidates for next-generation optoelectronic devices, including tunable emitters and detectors. ZnSe nanowire-based devices show great promise in blue emission applications, since they can be easily and reproducibly fabricated. However, their utility is limited by deep level defect states that inhibit optoelectronic device performance. The primary objective of this work is to show how the performance of ZnSe nanowire devices improves when nanowires are subjected to a post-growth anneal treatment in a zinc-rich atmosphere. We use low temperature photoluminescence spectroscopy to determine the primary recombination mechanisms and associated defect states. We then characterize the electronic properties of ZnSe nanowire field effect transistors fabricated from both as-grown and Znannealed nanowires, and measure an order-of-magnitude improvement to the electrical conductivity and mobility after the annealing treatment. We show that annealing reduces the concentration of zinc vacancies, which are responsible for strong compensation and high amounts of scattering in the as-grown nanowires.
“…These results support the idea that molecular vibrations and semiconductor defect levels are being probed in the SFG NSOM measurements. Comparison of the experimental IR and SF energies with defect energy measurements obtained by capacitance techniques, however, is difficult due to large variation in reported values and assignments. ,, These disparities may result from details of sample preparation methods, the precision of the different techniques employed, and variation in semiconductor models. 6 SFG and SHG NSOM of CVD ZnSe.…”
Section: Sum Frequency Generation Nsommentioning
confidence: 99%
“…Comparison of the experimental IR and SF energies with defect energy measurements obtained by capacitance techniques, however, is difficult due to large variation in reported values and assignments. 108,110,111 These disparities may result from details of sample preparation methods, the precision of the different techniques employed, and variation in semiconductor models.…”
The emerging field of coherent nonlinear near-field scanning optical microscopy (NSOM) is reviewed. Second harmonic, third harmonic, and sum frequency generation (SHG, THG, and SFG) are explored as means of providing chemically and environmentally selective probes with nanometer spatial resolution provided by scanning probe microscopy. Chemical selectivity is generated via resonant enhancement of the nonlinear signals, whereas interface vs bulk contrast is achieved by the order (even vs odd) of the optical process. A method of producing higher spectral resolution, and thus increased chemical selectivity, is also demonstrated in the form of near-field detected multiplex (or "broad-bandwidth") SFG (MSFG). Applications to biological and material samples are described.
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