Abstract: An optical device such as a radiation detector or an optically activated memory includes a barrier region located between two active regions. One or more quantum dots are provided such that a change in the charging state of the quantum dot or dots affects the flow of current through the barrier region. The charging states of the quantum dot is changed by an optical device.

Abstract: An optical device such as a radiation detector or an optically activated memory comprises a barrier region (11) located between two active regions (9, 15). One or more quantum dots (21) are provided such that a change in the charging state of the quantum dot or dots (21) affects the flow of current through the barrier region (11). The charging states of the quantum dot is changed by optical means.

Abstract: A semiconductor device is presented which exhibits both interband and intraband tunnelling. The device comprises two active layers (21, 23) which are sandwiched between two barrier layers (3, 5). These layers are located between first and second terminals (7, 9). The active layers (21, 23) are chosen such that the conduction band edge (27) of the first active layer (21) having a lower energy than the valence band edge (25) of the second active layer (23);the first active layer (21) having a first confined conduction band energy level (29) with an energy higher than that of the conduction band edge (27) of the first active layer (21);the second active layer (23) having a first confined valence band energy level (33) with an energy lower than that of the valence band edge (25) of the second active layer (23);wherein the first confined valence band energy level (33) and the first confined conduction band energy level (29) are located such that the device can exhibit both intraband and interband tunnelling.