Preparation and Properties of Amorphous Boron Films Deposited by Pyrolysis of Decaborane in the Molecular Flow Region

Abstract

Boron films of 0.1–1.5 μm thickness have been prepared on sapphire, silicon, and tantalum as substrates by the pyrolysis of decaborane in the molecular flow region (≦10−4 torr) and in a temperature range of 350°–1200°C. It is found that the deposition rate of the boron films is proportional to the decaborane partial pressure and the substrate temperature. Below 416°C, the deposition rate is given as a function of the substrate temperature and partial pressure of decaborane. This relation is where is the substrate temperature, is the pressure of decaborne, and is the gas constant. The apparent activation energy for the decomposition of decaborane is found to be 39 kcal/mol. X‐ray and electron diffraction study indicates that the films are amorphous. The electrical conductivities vary from at 77 K to 30 S · cm−1 at 1000 K, and the activation energy is 1.07 eV in the intrinsic temperature range (700–1000 K). The maximum value of thermo‐electric power is about 420 μV · deg−1 at 700 K, and its polarity is positive between 500 and 1000 K. The absorption coefficient, refractive index, and extinction coefficient of boron films are obtained from the measured transmittance and reflectance. The energy of the indirect allowed transition is estimated to be .