Electrical investigation of the Al/porous Si/p+-Si heterojunction

Porous silicon based Al/porous Si/p+-Si heterojunction with porous silicon layer was fabricated on low-resistivity crystalline silicon substrate by electrochemical anodisation. Measurements of the current–voltage I(V) characteristics and capacitance–voltage C(V) at various frequencies were used for the investigation of the electrical properties of this heterojunction. The forward bias I(V) dependencies exhibited a high value of the quality factor close to 7. This was attributed to the existence of interfacial layer and interface states which cause the forward I(V) characteristic not to obey the ideal Schottky diode characteristic. Therefore, it was demonstrated that the current has a square root dependence on the forward bias and it was governed by the Richardson–Schottky conduction mechanism. Furthermore, an ideality factor near the unity has been obtained in the reverse current and the I(V) characteristics were governed by the porous Si/Si heterojunction.The C(V) measurement was performed at different frequencies and revealed that the capacitance behavior was typical of material with interface states. The density of interface states was found to vary from 2×1010 eV−1cm−2 to 1.1×1011 eV−1cm−2 as a function of the interface states energy level position in the band gap of the porous silicon.