Comment on: On shallow-deep instability of impurity level in semiconductors

It is pointed out that a correct form and also a more general form of the model introduced by Mukhopadhyay in the problem of shallow-deep instability of impurity ground level in semiconductors have, in fact, been introduced long ago by various authors to study the same problem. The models have also been solved for the ground state by various methods such as variational (with better variational trial function than that of Mukhopadhyay) and numerical. Recently we have solved the problem analytically for all the states.