DIELECTRIC-PROPERTIES OF ALN FILMS PREPARED BY LASER-INDUCED CHEMICAL-VAPOR-DEPOSITION

The dielectric properties and electrical conductivity of AlN films dep osited by laser-induced chemical vapour deposition (LCVD) are studied For a range of growth conditions. The static dielectric constant is 8. 0 +/- 0.2 over the frequency range 10(2)-10(7) Hz and breakdown electr ic fields better than 10(6) V cm(-1) are found for all films grown at temperatures above 130 degrees C. The resistivity of the films grown u nder optimum conditions (substrate temperature above 170 degrees C, NH 3/TMA flow rate ratio greater than 300 and a deposition pressure of 1- 2 Torr) is about 10(14) Omega cm and two conduction mechanisms can be identified. At low fields, F < 5 x 10(5) V cm(-1) and conductivity is ohmic with a temperature dependence showing a thermal activation energ y of 50-100 meV, compatible with the presumed shallow donor-like state s. At high fields, F > 1 x 10(6) V cm(-1), a Poole-Frenkel (field-indu ced emission) process dominates, with electrons activated from traps a t about 0.7-1.2 eV below the conduction band edge. A trap in this dept h region is well-known in AlN. At fields between 4 and 7 x 10(5) V cm( -1) both conduction paths contribute significantly. The degradation of properties under non-ideal growth conditions of low temperature or lo w precursor V/III ratio is described.