Electronic Properties of Diamond

Diamond’s potential as an electronic material has become legendary by virtue of its wide band gap (5.5eV), high carrier mobility, breakdown field, saturation velocity, and thermal conductivity.  If this potential can be realized, diamond is ideally suited as the material for devices which operate at high temperatures, voltages, power levels, and frequencies, as well as in high-radiation environments.  The electrical resistivity of natural diamond is as high as 1015 ohm-cm and that of homoepitaxial CVD diamond films is equally high.  The potential of diamond as a material for solid state devices has been the subject of a number of reviews [9-13].

As a semiconductor, the properties of diamond (except for electron mobility) are virtually unexcelled.  Of semiconductors currently in use, only germanium (Ge) and indium antimonide (InSb) exhibit superior hole mobilities.  Even then, these materials exhibit poor saturated hole velocities and low dielectric strength.

The wide band gap (5.5ev) of diamond simultaneously makes it an excellent insulator and an unusably resistive semiconductor.  With doping, the intrinsic properties of diamond can be manipulated into practical energetic states.  Boron has been identified as the dopant responsible for p-type behavior in naturally occurring semiconducting diamond [10].  From geometric and energetic considerations, boron is likely the only element that can substitutionally dope diamond without large distortions to the lattice.  Nitrogen, a commonly occurring impurity in diamond, is electrically inactive, although it acts as a recombination center [10].   A theoretical study by Kajihara et al [16] suggests the potential of P, Li, and Na as shallow n-type dopants.  Phosphorus is theorized to occupy a substitutional site, while lithium and sodium are expected to reside in interstitial positions.  Recent work on phosphorous doping has met with some success [17].  

CVD deposited diamond films necessarily contain hydrogen, as it is an essential component of the plasma growth environment.  Hydrogen is known to reduce the resistivity to the order of 106 Ω-cm.  Annealing in a hydrogen-free environment allows hydrogen to diffuse out of the film, increasing resistivity by a few orders of magnitude [18, 19].  Exposure to hydrogen reversibly reduces the resistivity to as-deposited values.  An improved understanding of hydrogen effects in diamond films would certainly contribute to tighter control over electrical properties.

 

9.         Keyes, R.W., Figure-of-merit for semiconductors for high speed switches. Proc. IEEE, 1972. 60.

10.       Collins, A.T. and Lightowlers, E.C., The Properties of Diamond, ed. J.E. Field. 1979, San Diego: Academic Press.

11.       Shenai, K., Scott, R.S., and Baliga, B.J., Optimum Semiconductors for High Power Electronics. IEEE Transactions on Electron Devices, 1989. 36.

12.       Geis, M.W., Efremow, N.N., Woodhouse, J.D., et al., Diamond cold cathode. Electron Device Letters, IEEE, 1991. 12(8): p. 456-459.

13.       Trew, R.J., Yan, J.B., and Mock, P.M., The potential of diamond and SiC electronic devices for ... and millimeter-wave power applications. Proc. IEEE, 1991. 79.

14.       Buberman, G.S., The Band Structure of Diamond. Soviet Physics Uspekhi, 1971. 14(2).

15.       Herman, F., Kortum, R.L., and Kuglin, C.D., Energy band structure of diamond, cubic silicon carbide, silicon, and germanium. International Journal of Quantum Chemistry, 1967. 1(S1): p. 533-566.

16.       Kajihara, S.A., Antonelli, A., and Bernholc, J. in Diamond, Silicon Carbide, and Related Wide Bandgap Semiconductors. 1990: Material Research Society.

17.       Lazea, A., Barjon, J., DHaen, J., et al., Incorporation of phosphorus donors in (110)-textured polycrystalline diamond. Journal of Applied Physics, 2009. 105(8): p. 083545.

18.       Landstrass, M.I. and Ravi, K.V., Resistivity of chemical vapor deposited diamond films. Applied Physics Letters, 1989. 55(10).

19.       Albin, S. and Watkins, L., Current-voltage characteristics of thin film and bulk diamond treated in hydrogen plasma. IEEE Electron Device Letters, 1990. 11(4): p. 159-161.

News