Photodetector

A method of manufacturing a photodetector device, the method comprising:

• fabricating first and second light absorbing regions using semiconductor material doped respectively n-type and p-type, wherein the first and second light absorbing regions are fabricated as respective epitaxial layers arranged on top of one another in relation to a substrate, wherein the light absorbing regions are configured to generate pairs of electrons and holes in response to absorption of photons when light is incident on the device;
• fabricating first and second contact regions composed of semiconductor material and which are doped respectively p-type and n-type, wherein the contact regions have higher doping concentrations than the light absorbing regions, and are labelled as p+ and n+ respectively;
• and
• providing first and second contacts connected to the first and second contact regions respectively,
• wherein the n-type and p-type light absorbing regions and the n+ and p+ contact regions are arranged in a sequence n+p n p+ so that, after a voltage applied between the n+ and p+ contacts is switched from a reverse bias to a forward bias, electrons and holes which are generated in the light absorbing regions in response to photon absorption drift towards the p+ and n+ contact regions respectively, which causes current to start to flow between the contacts after a time delay which is inversely proportional to the incident light intensity.

A method of operating a photodetector device, the method comprising:

• providing a photodetector device with:
• first and second light absorbing regions composed of semiconductor material doped respectively n-type and p-type, wherein the first and second light absorbing regions are fabricated as respective epitaxial layers arranged on top of one another in relation to a substrate, wherein the light absorbing regions are configured to generate pairs of electrons and holes in response to absorption of photons when light is incident on the device;
• first and second contact regions composed of semiconductor material and doped respectively p-type and n-type, wherein the contact regions have higher doping concentrations than the light absorbing regions, and are labelled as p+ and n+ respectively;
• and
• first and second contacts connected to the first and second contact regions respectively, wherein the n-type and p-type light absorbing regions and the n+ and p+ contact regions are arranged in a sequence n+p n p+;
• and
• operating the photodetector device by repeatedly:
• applying a voltage to reverse bias the n+ and p+ contacts;
• switching the reverse bias voltage to a forward bias voltage so that after said switching electrons and holes which are generated in the light absorbing regions in response to photon absorption drift towards the p+ and n+ contact regions respectively;
• and
• sensing for onset of current flow between the first and second contacts and measuring a time delay between said switching and said onset, wherein the time delay is inversely proportional to the incident light intensity.