Insulator to metallic transition due to intermediate band formation in Ti-implanted silicon

Abstract

We have analyzed by means of electrical transport measurements, the insulator to metallic transition due to intermediate band (IB) formation (insulator to metallic-IB) in silicon layers. The samples were implanted with titanium concentrations well above the solid solubility limit and subsequently pulsed laser melted (PLM). Whereas the doping of silicon with Ti impurity concentrations below the Mott limit is known to produce deep levels which act as non radiative recombination centers, the introduction of a high concentration of deep impurities above this limit could form an IB. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) measurements show the remaining titanium concentration profile after PLM, indicating whether this concentration is above or below the theoretical limit for IB formation in the different implanted samples. Sheet resistance and Hall effect measurements performed in the temperature range (100–300K) show that insulator to metallic-IB transition takes place for concentrations above ∼1020cm−3. This transition becomes apparent in a rectifying behavior observed in van der Pauw and transversal I–V electrical measurements at low temperatures. Contacts exhibit Schottky or ohmic behavior for samples with Ti concentrations below or above the transition, respectively. All these results point out to the metallic behavior of the IB and provide a powerful tool to determine the IB formation in a semiconductor.