Hideyo Okushi

Electrical properties of n‐amorphous/p‐crystalline silicon heterojunctions

We have measured C‐V characteristics and temperature dependence of J‐V characteristics of undoped hydrogenated amorphous silicon (a‐Si:H) heterojunctions formed on p‐type crystalline silicon ( p c‐Si) substrates with different resistivities. It has been found that an abrupt heterojunction model is valid for a‐Si:H/p c‐Si heterojunctions, and the electron affinity of a‐Si:H has been estimated as 3.93±0.07 eV from C‐V characteristics. The forward current of all the junctions studied shows voltage and temperature dependence expressed as exp(−ΔEa f/kT) exp(AV), where ΔEa f and A are constants independent of voltage and temperature, being successfully explained by a multitunneling capture‐emission model. The reverse current is proportional to exp(−ΔEar/kT)(VD−V)1/2, where VD is the diffusion voltage and ΔEar is a constant. This current is probably limited by generation‐recombination process.

Investigation of the effect of hydrogen on electrical and optical properties in chemical vapor deposited on homoepitaxial diamond films

We have investigated electrical and optical properties of the high-conductivity layers formed in both undoped and B-doped diamond films prepared by chemical vapor deposition. It is found that both hydrogenated undoped and B-doped diamond films have high-concentration holes of ∼1018 cm−3 at 297 K. These films exhibit little temperature dependence of the hole concentration between 120 and 400 K, while that of the oxidized B-doped film has a strong temperature dependence with an activation energy 0.38 eV. The Hall mobility of all the hydrogenated films of ∼30 cm2/Vs at 297 K is one to two orders of magnitude smaller than that of the oxidized B-doped film and increases with increasing temperature. The I−V characteristics of Al–Schottky contacts to the hydrogenated undoped film show excellent rectification properties and the temperature dependence of their forward characteristics is well explained by a junction theory inclusive of the tunneling process, i.e., thermionic-field emission theory, indicating that t...

STUDY OF THE EFFECT OF HYDROGEN ON TRANSPORT PROPERTIES IN CHEMICAL VAPOR DEPOSITED DIAMOND FILMS BY HALL MEASUREMENTS

Using Hall effect measurements, we have investigated carrier transport in a high‐conductivity layer formed in the surface region of as‐deposited homoepitaxial diamond films prepared by chemical vapor deposition. The results of undoped and B‐doped films were compared to those obtained from an oxidized B‐doped film. It is found that (1) the carrier (hole) density per unit area of both as‐deposited films is 4–5 orders of magnitude larger than that of the oxidized B‐doped film at 297 K and is nearly constant in the temperature range of 150–400 K, while that of the oxidized B‐doped film shows a strong temperature dependence with an activation energy of 0.38 eV, and (2) the Hall mobility of both as‐deposited films is 1–2 orders of magnitude smaller than that of the oxidized B‐doped film at 297 K and increases with increasing temperature, while that of the oxidized B‐doped film decreases. These results and the secondary ion mass spectroscopy analysis suggest that the high‐conductivity layer formed in the as‐depo...

Electrical and Structural Properties of Phosphorous-Doped Glow-Discharge Si:F:H and Si:H Films

Doping of Si:F:H and Si:H with P has been performed by a glow-discharge technique using PH3/SiF4+H2, PF5/SiF4+H2, PH3/SiH4+H2 and PF5/SiH4+H2 gaseous mixtures, and high conductive films over 100 ?-1 cm-1 have been obtained. It has also been made clear from X-ray diffraction and Raman-scattering measurements that all the P-doped Si:F:H films (P/Si>5?10-4) as well as high conductive Si:H films deposited under high RF power condition are polycrystalline, while Si:H films prepared under low power remain amorphous and their conductivity is less than 10-2 ?-1 cm-1. It is likely that film conductivity amounting to 100 ?-1 cm-1 should be ascribed to its polycrystalline structure.

n-type doping of (001)-oriented single-crystalline diamond by phosphorus

n-type doping of (001)-oriented single-crystalline diamond has been achieved using PH3 as doping gas and applying a newly optimized homoepitaxial growth technique based on plasma-enhanced chemical vapor deposition. Hall-effect measurements indicate n-type conductivity with highest mobilities of ∼350cm2∕Vs. Phosphorus doping is confirmed by secondary-ion mass spectroscopy.

Direct observation of negative electron affinity in hydrogen-terminated diamond surfaces

Total photoyield experiments are applied to characterize p-, intrinsic, and n-type diamond with hydrogen-terminated surfaces. On all hydrogen-terminated samples a photoelectron threshold energy of 4.4 eV is detected which is discussed in detail in this letter. We attribute this threshold to the energy gap between the valence-band maximum and the vacuum level, which is 1.1 eV below the conduction-band minimum, and generally referred to as ”negative electron affinity” (NEA). Hydrogen terminated p-type and intrinsic diamond show a rise of secondary photoyield in the excitation regime hν>5.47eV. However, this is not detected on n-type diamond. We ascribe this to the formation of an upward surface band bending in the vicinity of the n-type diamond surface which acts as an energy barrier for electrons.

Isothermal Capacitance Transient Spectroscopy for Determination of Deep Level Parameters

A new measurement method for deep levels in semiconductors is proposed, by which the measurement of the transient change of capacitance is performed under an isothermal condition (Isothermal Capacitance Transient Spectroscopy). The method allows us to construct a precise measurement and analysis system by a programmable calculator. Computer simulation and experiment by the method in the case of Au-doped Si are demonstrated. It is shown that the method is one of useful tools for spectroscopic analysis of deep levels in semiconductors.

High-Quality B-Doped Homoepitaxial Diamond Films using Trimethylboron

High-quality B-doped homoepitaxial diamond films have been synthesized by microwave plasma chemical-vapor-deposition (CVD) using a mixture consisting of CH4, H2, and trimethylboron B(CH3)3 diluted by H2 gas. These films have been obtained on the basis of the approach that high-quality diamond films should be grown in a clean CVD system. Hall-effect measurements of the film show that the Hall mobility exceeds about 1800 cm2/Vs when the hole concentration is 2.3×1014 cm-3 at room temperature (290 K) and about 3300 cm2/Vs at 170 K. These results indicate that the quality of the present B-doped CVD films is comparable with or better than that of high-quality natural diamonds.

Strong excitonic recombination radiation from homoepitaxial diamond thin films at room temperature

We have observed strong emission lines at 5.27 and 5.12 eV at room temperature in cathodoluminescence spectra from homoepitaxial diamond films grown by step-flow mode prepared with microwave plasma assisted chemical vapor deposition. The temperature dependence of integrated intensity of the emission lines indicates that they are attributed to free-exciton recombination radiation associated with a transverse optical phonon and its replica. These results have demonstrated the superior crystalline quality of the homoepitaxial diamond films grown by the step-flow mode.

Intrinsic electrical properties of Au/SrTiO3 Schottky junctions

Intrinsic electrical properties of Au/Nb-doped SrTiO3(001) (STO:Nb) Schottky junctions, fabricated using a proper surface treatment of the STO:Nb and in situ deposition of Au, were investigated in detail. Current–voltage characteristics and photocurrent–wavelength characteristics have shown a temperature-dependent and voltage-dependent Schottky barrier height, while capacitance–voltage characteristics have shown a temperature-independent flat band voltage. Using a temperature-dependent and field-dependent permittivity of the STO in the framework of Devonshire theory, we have performed computer simulation of the Schottky barrier potential to analyze the electrical properties of the junction. It is found that an intrinsic low permittivity layer at the Au/STO:Nb interface explains all the temperature dependence of the electrical properties.