L.S. Pan

Diamond : electronic properties and applications

1: Electronic and Vibrational Properties of Bulk Diamond C.Y. Fong, B.M. Klein. 2: Diamond Surface B. Pate. 3: Growth of CVD Diamond for Electronic Applications L.S. Plano. 4: Doped Diamonds K. Okano. 5: Defects in Diamond W. Zhu. 6: Free Carrier Dynamics in Diamond S. Han, L.S. Pan, D.R. Kania. 7: Thermal Conductivity of Diamond J.E. Graebner. 8: Electrical Contacts to Diamond T. Tachibana, J. Glass. 9: Electronic Device Processing M.A. Plano. 10: Passive Diamond Electronic Devices D.L. Freifus. 11: Active Diamond Electronic Devices S. Grot. Appendix: Table A1. Properties of Semiconductors at 293 K. Index.

Diamond radiation detectors

Abstract Diamond radiation detectors have a lengthy history. Photoconductive UV detectors were developed in the 1920s and ionizing radiation detectors were created in the 1940s. However, these devices encountered restricted usage owing to the limitations of natural diamonds. Specifically, these limitations were the small size and lack of control of the material characteristics. Recent advances in the high quality growth of diamond by chemical vapor deposition have created the opportunity for the application of this material in practical detectors.

Device properties of homoepitaxially grown diamond

Homoepitaxial single-crystal diamond layers were grown on naturally occurring type Ia and IIa gemstone diamond substrates using microwave-plasma-assisted chemical vapor deposition techniques. The epitaxial layers ranged in thickness from 0.5 to 800 μm. Single crystals were grown both unintentionally doped and intentionally doped by means of gas phase dopants. Planar photoconductive diodes were fabricated from the high resistivity crystals and junction diodes were fabricated from the boron-doped crystal layers. The photoconductive diode response was measured and the output signals were analyzed to derive the carrier mobility and lifetime. Combined carrier photoconductive mobility values exceeded 3500 cm2 V−1s−1, only seen in the best IIa gemstone diamonds. Junction diodes yielded the highest breakdown fields with typical values in excess of 2 × 107 V cm−1 dielectric strength.

Particle‐ and photoinduced conductivity in type‐IIa diamonds

Electrical characteristics associated with radiation detection were measured on single‐crystal natural type‐IIa diamond using two techniques: charged particle‐induced conductivity and time‐resolved transient photoinduced conductivity. The two techniques complement each other: The charged particle‐induced conductivity technique measures the product of the carrier mobility μ and lifetime τ throughout the bulk of the material while the transient photoconductivity technique measures the carrier mobility and lifetime independently at the first few micrometers of the material surface. For each technique, the μτ product was determined by integration of the respective signals. The collection distance that a free carrier drifts in an electric field was extracted by each technique. As a result, a direct comparison of bulk and surface electrical properties was performed. The data from these two techniques are in agreement, indicating no difference in the electrical properties between the bulk and the surface of the ...

Absolute x‐ray power measurements with subnanosecond time resolution using type IIa diamond photoconductors

Photoconductive devices have been fabricated from type IIa diamonds. The sensitivity of these devices is independent of photon energy from 200 to 2200 eV. The dynamic range is 105. The large band gap of the diamond greatly reduces the sensitivity to photons with an energy less than 5.5 eV which is an attractive feature for many applications. The carrier lifetime in the material is 90 ps and the mobility is 1650 cm2/V/s at 106 V/m.

THICKNESS DEPENDENCE OF THE ELECTRICAL CHARACTERISTICS OF CHEMICAL VAPOR DEPOSITED DIAMOND FILMS

The electrical characteristics of chemically vapor deposited (CVD) diamond films were measured as a function of film thickness. The samples studied were polycrystalline with the average grain size increasing from approximately 1 μm on the substrate side to approximately 30 μm on the growth surface for the thickest sample. Using time‐resolved transient photoconductivity and charged‐particle induced conductivity, the collection distance (d) that a free carrier drifts under the influence of an applied electric field was measured. Our data indicate that there is a gradient in the collection distance through the material. This gradient in electrical properties has implications for electronic uses of CVD diamond.

First measurements with a diamond microstrip detector

Abstract We have constructed the first high resolution strip detector using chemical vapor deposited diamond as the detection medium. Devices produced with this material have the possibility of being extremely radiation hard with direct applications at high luminosity colliders. This paper details the detector material, the low noise readout electronics and the detector module. First results from a test with high momentum charged particles in a testbeam at CERN are described. We achieved a signal-to-noise of 6:1 and an efficiency of 85% for minimum ionizing particles in the testbeam. The detector has a strip pitch of 100 μm and a strip width of 50 μm. The measured position resolution we achieved was σ = 26 μm. Future development of diamond detectors with application in particle physics experiments and other fields is discussed.

Polycrystalline CVD diamond films with high electrical mobility

Advances in the deposition process have led to dramatic improvements in the electronic properties of polycrystalline diamond films produced by chemical vapor deposition (CVD). It is now possible to produce CVD diamond with properties approaching those of IIa natural diamonds. The combined electron-hole mobility, as measured by transient photoconductivity at low carrier density, is 4000 square centimeters per volt per second at an electric field of 200 volts per centimeter and is comparable to that of the best single-crystal IIa natural diamonds. Carrier lifetimes measured under the same conditions are 150 picoseconds for the CVD diamond and 300 picoseconds for single-crystal diamond. The collection distance at a field of 10 kilovolts per centimeter is 15 micrometers for the CVD diamond as compared to 30 micrometers for natural diamonds. The electrical qualities appear to correlate with the width of the diamond Raman peak. Also, although the collection distance at the highest fields in the films nearly equals the average grain size, there is no evidence of deleterious grain boundary effects.

Electrical properties of high quality diamond films

Abstract Significant improvements have been made over the last year in the quality of chemical vapor deposited (CVD) diamond films. In particular, efforts have been made to improve the mobilities and lifetimes of free carriers. Values as high as 4000 cm 2 per V-s have been measured for the combined electron and hole mobilities in the best polycrystalline diamond, which is comparable to that of the best single-crystal IIa natural diamonds. Comparable carrier lifetimes have also been observed, ranging from 150 ps to 1 ns in CVD diamond, compared with 100 to 600 ps in natural IIa diamonds. The films were produced by microwave-assisted CVD, and both polycrystalline and epitaxial films were studied. The carrier mobility and lifetime were measured using transient photoconductivity as a function of electric field and excitation density. Both velocity saturation and electron-hole scattering were observed in the CVD films, similar to behavior measured in natural diamonds. The drift distance at an electric field of 10 kV cm −1 was as high as 15 μm. The improved properties are most likely due to lowered defect densities. Comparable results between epitaxial and polycrystalline films suggest that structural defects may not be the limitation. The improved quality is a significant step toward the production of electronic devices made of diamond, in particular diamond detectors for ionizing radiation. Already CVD diamond has been used to detect ultraviolet light, X-rays and high energy charged particles.

Soft x‐ray detection with diamond photoconductive detectors

Photoconductive detectors (PCDs) fabricated from natural IIa diamonds have been used to measure the x‐ray power emitted from laser‐produced plasmas. The detector was operated without any absorbing filters which distort the x‐ray power measurement. The 5.5 eV band gap of the detector material practically eliminates its sensitivity to scattered laser radiation thus permitting filterless operation. Excellent agreement was achieved between a diamond PCD and a multichannel photoemissive diode array in the measurement of radiated x‐ray power and energy.