Photoemission Of Holes Research Articles

Photovoltaic properties and barrier heights of single-crystal and polycrystalline Cu2O–Cu contacts

The spectral distribution of the photovoltaic response of polycrystalline and single-crystal Cu2O–Cu contacts was measured at room temperature using a chopped light technique. The single-crystal contacts were formed by reducing the (111) surface of single-crystal Cu2O to copper using atomic hydrogen at room temperature. Prior to the reduction, a departure from stoichiometry was induced in the single crystals by treatment at 750 or 960°C in a known and controllable partial pressure of oxygen. The polycrystalline contacts were prepared from polycrystalline copper plate partially oxidized to Cu2O at 1000°C. The photoresponse measurements indicate that the dominant photovoltaic mechanisms in Cu2O–Cu contacts are hole photoemission from Cu into Cu2O when hv < Eg and electron injection from Cu2O into Cu when hv > Eg. Barrier heights determined from the threshold of the hole photoemission process measured 0.75±0.06 eV for the single-crystal contacts and 0.75±0.02 eV for the polycrystalline contacts. It is shown that the observed variation in the barrier height of the single-crystal contacts may be due to barrier lowering by the Schottky effect.

Internal photoemission: CdS-PVK and CdSe-PVK

The electric field and temperature dependence of the quantum gain associated with the internal photoemission of holes from CdS and CdSe into poly(N-vinyl carbazole), i.e., PVK, are discussed in terms of a simple model of energy-loss scattering by holes near the PVK surface. Excellent qualitative agreement is obtained between simple analytical expressions derived on the model and data on CdS-PVK and CdSe-PVK.

Hole Photoemission from CdS, CdSe, HgS, and Se into Sulfur Single Crystals

Hole photoemission from CdS, CdSe, HgS, and Se into sulfur single crystals has been observed. The hole quantum efficiency ($Y$) was measured as a function of the photon energy ($\ensuremath{\hbar}\ensuremath{\omega}$) in the range 2.11-3.54 eV at room temperature. Our results fit the equation ${Y}^{\frac{1}{2}}=A\ensuremath{\hbar}(\ensuremath{\omega}\ensuremath{-}{\ensuremath{\omega}}_{0})$ for ${\ensuremath{\omega}}_{0}l\ensuremath{\omega}l{\ensuremath{\omega}}_{1}$ and ${Y}^{\frac{1}{2}}={[{A}^{2}{\ensuremath{\hbar}}^{2}{(\ensuremath{\omega}\ensuremath{-}{\ensuremath{\omega}}_{0})}^{2}+{B}^{2}{\ensuremath{\hbar}}^{2}{(\ensuremath{\omega}\ensuremath{-}{\ensuremath{\omega}}_{1})}^{2}]}^{\frac{1}{2}}$ for $\ensuremath{\omega}g{\ensuremath{\omega}}_{1}$, where $A$, $B$, ${\ensuremath{\omega}}_{0}$, and ${\ensuremath{\omega}}_{1}$ are adjustable parameters. The threshold energies $h{\ensuremath{\omega}}_{0}$ and $h{\ensuremath{\omega}}_{1}$ vary from one emitter to the other as one would expect for junctions with different band-energy relations at the interface. However the difference $\ensuremath{\hbar}({\ensuremath{\omega}}_{1}\ensuremath{-}{\ensuremath{\omega}}_{0})=0.48\ifmmode\pm\else\textpm\fi{}0.04$ eV and the relation $\frac{B}{A}=2.1\ifmmode\pm\else\textpm\fi{}0.3$ seem to be independent of the emitter. These results can be understood if one identifies $\ensuremath{\hbar}({\ensuremath{\omega}}_{1}\ensuremath{-}{\ensuremath{\omega}}_{0})$ with the energy difference between the tops of the two overlapping valence bands of sulfur reported previously by Cook and Spear.

Internal photoemission of holes and electrons into KN 3

Holes and electrons have been photoinjected into single crystals of KN 3 from both gold and silver electrodes. For gold the injection thresholds for electrons and holes were 4.4 ± 0.1 and 3.92 ± 0.15 eV respectively and for silver electrodes 4.0 ± 0.1 eV and 4.44 ± 0.15 eV. From these values a band gap of 8.44 ± 0.25 eV is obtained for KN 3. The μτ product for electrons at room temperature was found to be (1.8 ± 0.2) × 10 −4 cm 2/V. For holes μτ ≈ (6±2) × 10 −5 cm 2/V.

Transient Photoconductivity Effects in an Insulator-Semiconductor Powder System

An investigation of transient photoconductivity effects associated with semiconductor particles suspended in a transparent insulator has been carried out. II-VI compound crystalline solid solutions of CdSxSe1−x and CdSeyTe1−y were used as the photoconductors and poly (N-vinyl carbazole), PVK, as the transport medium, or matrix. Interparticle distances (∼ 5 μ) were large compared with particle diameters (∼ 1 μ). Transient photoconductivity as well as xerographic discharge measurement techniques were employed to study the quantum yield of the system as a function of applied electric field, wavelength of the incident radiation, temperature, and certain surface parameters of the components. Ideal geometry samples, consisting of single-crystal semiconductor-PVK-metal capacitors, were also studied to observe directly the photoemission of holes from the semiconductor into the PVK. The magnitude of the injection efficiency is found to depend upon the surface parameters of the components as well as the applied electric field. The data indicate the electric field dependence of the discharge in these systems to be due to electric field penetration of the surface of the semiconductor.

PHOTORESPONSE CHARACTERISTICS OF EXTENDED SURFACE-BARRIER DIODES

Surface-barrier diodes, which show a reversal of the photoresponse polarity with changing photon energy, have been fabricated by diffusing Cu into heavily n-type GaAs. The photoresponse is found to depend strongly upon applied bias. These properties are explained in terms of a model in which a thin compensated region at the semiconductor surface allows the simultaneous photoemission of both holes and electrons from the metal into the semiconductor.

Photoemission of Holes and Valence Band Structure in Anthracene

Abstract Recent measurements of the Hall effect for volume-generated holes in anthracene and analysis of the differences between Hall and drift mobility values for electrons and holes suggest that both carriers move in a two-band system; a narrow band where the mobility is of the order of 1 cm2v−1 sec−1 separated from a much wider band with high mobility by an energy of the order of 0.05 eV.(1) For electrons, the existence of wider bands has been well established by internal photoemission.(2,3) The conduction band system consists of a narrow band, less than 0.33 eV wide, separated by less than 0.05 eV from a higher band 0.3 eV wide.(3)

Photoemission of Holes and Electrons from Aluminum into Aluminum Oxide

The photoemission of both electrons and holes from aluminum into thin layers of ``plasma-grown'' aluminum oxide has been observed. The threshold energies for these processes are found to be 2.0±0.2 eV for electrons and 3.1±0.2 eV for holes. An approximate energy band diagram of the Al–Al2O3 interface based on these values is presented.

Steady state and transient photoemission into amorphous insulators

Steady state and transient photoemission of carriers from metal electrodes has been used to study the electronic energy level structure and transport properties of two amorphous insulators, the polymer poly-n-vinyl carbazole (PVK) and amorphous selenium. The results for these two materials illustrate different types of information which these combined techniques can give. Fine structure on the steady state spectral response of the photoemission for PVK is identified with vibrational splitting of the valence band which is < 0.1 eV wide. The time resolve transport of holes photoemitted into this band reveals an effective hole mobility which is thermally activated and field dependent, with a value of about 10−7 cm2/V sec at 105 V/ cm and room temperature. For amorphous Se the transient photoemission of holes indicates a transition of the carrier supply from prredominantly internal photogeneration to photoemission. The dependence of the number of transported holes as a function of temperature and applied field shows a change in moving through this transition region. These results are significant with respect to the field dependent photogeneration of carriers in amorphous Se. The observed field dependent supply of photoemitted carriers is attributed to a general metal-insulator interface limitation commonly referred to as an unsaturated blocking contact.

Photoemission of Holes from Metals into the Organic Polymer Poly-N-Vinyl-Carbazole

Photoemission of Holes from Metals into the Organic Polymer Poly-N-Vinyl-Carbazole

Photoemission of Holes from Metals into the Organic Polymer Poly-N-Vinyl-Carbazole

Photoemission of Holes from Metals into the Organic Polymer Poly-N-Vinyl-Carbazole

PHOTOEMISSION OF ELECTRONS AND HOLES INTO SILICON NITRIDE

The photoemission of both electrons and holes from degenerate silicon into thin (160–270 Å) layers of silicon nitride has been observed. The threshold energies for these processes are found to be 3.17 ± 0.1 eV for electrons and 3.06 ± 0.1 eV for holes. In addition, the photoemission of electrons from aluminum into silicon nitride has been observed; the threshold energy in this case is 2.11 ± 0.1 eV. An approximate electron energy band diagram for silicon nitride based on these values is presented.

Internal Photoemission as a Tool for the Study of Insulators

Photoemission of electrons or holes from a conducting electrode into an adjoining insulator can be used to determine information about the energy‐band relationships at the interface between the conductor and the insulator and about carrier transport in the insulator. The basic theory of the measurement techniques is discussed, and some experiments employing these techniques (using silicon dioxide as the insulator) are described.

Surface States of Anthracene Crystals

The existence of surface states in anthracene crystals can be deduced from the thresh-old energies for photoemission of electrons or holes from various metals into anthracene. These surface states are capable of trapping electrons as well as holes; their density is about 2 \ifmmode\times\else\texttimes\fi{} ${10}^{13}$ ${\mathrm{cm}}^{\ensuremath{-}2}$ ${\mathrm{eV}}^{\ensuremath{-}1}$; their maximum depth is 1.3 \ifmmode\pm\else\textpm\fi{} 0.2 eV. They probably can act as recombination centers for charge carriers.

Determination of the band-gap in anthracene

From the threshold energies for photoemission of electrons and holes from Ce and Mg contacts into anthracene the band gap is found to be 3.72 ± 0.03 eV.

Photoemission of Holes from Metals into Anthracene

Photoemission of holes from metal electrodes into anthracene has been observed for Au, Ag, Al, Pb, and Mg. The photoemission of electrons into the anthracene from these metals could not be observed. From the variation of the photoemission threshold for holes with the work function of the metal a value of 5.80±0.34 eV was obtained for the energy of the valence band below the vacuum level; this value agrees with that determined by photoemission of electrons from anthracene into vacuum. The spectral response of the photoemission is complex; it appears to result from photoemission into a system of narrow bands arising from the interaction of molecular vibrations with a narrow electronic band. The experiment indicates that the energy bands are under 0.1 eV in width, as predicted by theory, and are broadened by vibrational overlap.

Photoemission of Holes from Silicon into Silicon Dioxide

Photoemission of holes from silicon into thermally grown silicon-dioxide layers has been observed. Measurements of the threshold energy for this effect are consistent with a value of about 4.92 eV for the energy difference between the conduction band edge in the silicon and the valence band edge in the oxide at the silicon-silicon-dioxide interface. The mean drift range (Schubweg) for holes in the oxide is much less than that for electrons. From measurements of the photocurrent versus electric field, it is inferred that for holes in the oxide valence band, the product of mobility and mean time before trapping is $\stackrel{\mathrm{\ensuremath{\sim}}}{&lt;}$ ${10}^{\ensuremath{-}14}$ ${\mathrm{m}}^{2}$/V.

Photoemission of holes from silicon into silicon dioxide

Photoemission of holes from silicon into silicon dioxide

Photoemission of Holes from Tin into Gallium Arsenide

Photoemission of Holes from Tin into Gallium Arsenide