Investigation of tellurium−implanted silicon

Abstract

Hall and sheet−resistivity measurements as a function of temperature combined with layer removal have been used to study Si implanted with Te at energies up to 220 keV. At low doses (≲4×1012 cm−2), Te has a donor level with a 140−meV activation energy. The activation energy decreases at higher Te doses and is approximately equal to zero for Te doses ≳1015 cm−2. At high dose levels, the number of conduction electrons per unit area Ns is more than an order of magnitude below the number of Te per unit area. High−temperature anneal treatments followed by quenching did not produce a substantial increase in Ns, suggesting that the formation of Te clusters was not responsible for the low value of Ns. Also, channeling measurements indicated a high substitutional fraction. Based on differential Hall measurements on samples implanted with phosphorus, with and without Si predamage, we conclude that residual radiation damage is not a major factor. A theoretical calculation, which includes the effect of decrease of activation energy with increasing impurity concentrations, indicated that the number of conduction electrons could be much less than the number of implanted Te even though the apparent activation energy is almost zero. Although the results of theoretical calculation do not give quantitative agreement with the experimental results, they do confirm the changes in apparent activation energy with concentration.