Formation of shallow acceptor states in the surface region of thin film diamond

Abstract

Considerable interest exists in fabrication of electronic devices from thin film polycrystalline diamond. To date, doping this material to achieve good free carrier concentrations and mobilities at room temperature has proved difficult. In this letter we report low temperature Hall effect measurements made on diamond films subjected to a hydrogenation process, such that the near surface region becomes p type without the addition of conventional dopant atoms. High carrier concentrations and mobilities can be achieved. The change in carrier concentration within the temperature range 10–300 K does not change as expected for most films, actually increasing as the temperature falls. This effect could be related to the confinement of carriers at the surface caused by the dipole provoked by adsorbed hydrogen on the diamond. However, polished films display more conventional behavior in that the carrier concentration falls with falling temperature.

n -type conductivity in ultrananocrystalline diamond films

“…p-type doping can be achieved with substitutional incorporation of boron, yielding an activation energy of 0.37 eV and, hence, fewer than 1% of the holes are activated at room temperature. 1 Hydrogen-induced surface conductivity can also be utilized to generate holes with an extremely low activation energy, 2,3 and high-performance devices have been demonstrated using this type of layer. 4,5 n-type doping has been much more elusive, with success in substitutional phosphorus doping achieved by relatively few laboratories; 6 an activation energy of 0.6 eV also makes phosphorus an unsuitable dopant for many applications.…”

Low Temperature Surface Conductivity of Hydrogenated Diamond

“…Note that the temperature during hydrogenation is a parameter which varies from laboratory to laboratory. Although in most cases temperatures between 750 and 850 C are utilized (for a review see [5]) it has been shown by Williams et al [14] that hydrogenation at 550 C also generates a highly conductive surface layer.…”

Homoepitaxial diamond growth for the control of surface conductive carrier transport properties

“…In fact, a single activation energy is rarely observed in the case of surface conductive diamond. 4,20 The room temperature value is among the highest recorded for surface conductive diamond. It can be seen from Fig.…”

“…Therefore, when hydrogenated, polycrystalline diamond films should be more resistive in general, and this is borne out in the empirical case. 2,4,18,23,24 Figure 8 demonstrates the reduction in sheet resistivity with substrate thickness. Initially these data are confusing, until one considers the fact that grain size increases with thickness in the case of polycrystalline diamond.…”

“…1 Early Hall measurements confirmed its nature as p-type 2 and subsequent investigations measured an extremely low activation energy. 3,4 High performance devices have been fabricated utilizing this surface conductive layer; [5][6][7][8][9] however its origin is still under debate. [10][11][12][13] As it is not a dopant in the conventional sense, control over the carrier transport values to date has been elusive.…”