Explain Schottky and Frenkel defects

Schottky barrier diode or hot-carrier diode, is a semiconductor diode formed by the junction of a semiconductor with a metal. It has a low forward voltage drop and a very fast switching action. When sufficient forward voltage is applied, a current flows in the forward direction.

A Frenkel defect is a type of point defect in crystalline solids named after its discoverer Yakov Frenkel. The defect forms when an atom or smaller ion leaves its place in the lattice, creating a vacancy, and becomes an interstitial by lodging in a nearby location.

it's all four options.