B. Rezek

Field emission mechanism of oxidized highly phosphorus-doped homoepitaxial diamond (111)

Spatially resolved electron field emission experiments on oxidized highly phosphorus-doped homoepitaxial diamond (111) were applied at room temperature. The diamond layer shows hopping conductivity. Field emission properties have three distinct regions. We attribute the variation in emission currents to: (a) Electron emission from conduction-band minimum (Region I), (b) Depletion of conduction-band electrons at the surface (Region II), and (c) emission from the phosphorus level (Region III). From these data, we calculate an effective positive electron affinity for the oxidized surface of 1–1.5eV.

High carrier mobility on hydrogen terminated ⟨100⟩ diamond surfaces

An increase in carrier mobility from typical values around 100 to more than 300cm2∕Vs at room temperature is detected on hydrogenated undoped ⟨100⟩ diamond layers after annealing at 400 K in a vacuum. As a function of temperature in the range 400 to 125 K the high mobility followed tendencies remarkably close ionized impurity (toward low temperatures) and phonon scattering (toward high temperatures). As a function of annealing time, the high mobility increased with the time constant of about 6.8 h in the range of 1–16 h. A prerequisite for obtaining the largest increase in mobility was optimized surface cleanness. Exposing the samples to air resulted in a complete recovery of the original values of mobility, hole concentration, and conductivity after several days. The data are discussed in terms of interactions between holes in the surface conductive channel and adsorbates on the surface.

Surface conductive layers on oxidized (111) diamonds

Surface conductive layers (SCL) on oxidized (111) diamonds with smooth surfaces after exposure to air were detected and characterized by Hall effect measurements. Hall effect measurements show that the conductivity is p type with sheet hole concentrations around of 1012cm−2 and Hall mobilities between 5 and 130cm2∕Vs. The SCL vanishes by thermal annealing at a temperature higher than 460K in He atmosphere, and recovers in air. These characteristics are similar to those generated by hydrogen termination. The experiments revealed that these SCLs are present on boron doped (111) and undoped (111) diamond films with smooth surfaces and natural IIa (111) diamonds, but not on (111) diamond films with rough surfaces and not on (100) diamonds.