Photodetector and method for fabricating the same

A photodetector comprising:

• a semi-insulating semiconductor substrate;
• a semiconductor conductive layer, which has been formed on a surface region of the substrate and has electrical conductivity;
• a light-absorbing layer, which absorbs light that has been incident on the photodetector;
• a carrier barrier layer, which has been formed between the conductive and light-absorbing layers to prevent carriers, created in the conductive layer, from diffusing and entering the light-absorbing layer;
• a wide bandgap layer, which has been formed on the light-absorbing layer and has a bandgap wider than a bandgap of the light-absorbing layer;
• and
• a doped region, which has been defined in the wide bandgap layer by doping part of the wide bandgap layer with a dopant that reaches the light-absorbing layer,
• wherein the conductive layer is made of InGaAsP and transmits part of the incident light with a particular wavelength.

A photodetector comprising:

• a semi-insulating semiconductor substrate;
• a semiconductor conductive layer, which has been formed on a surface region of the substrate and has electrical conductivity;
• a light-absorbing layer, which has been formed on the conductive layer and absorbs light that has been incident on the photodetector;
• a wide bandgap layer, which has been formed on the light-absorbing layer and has a bandgap wider than a bandgap of the light-absorbing layer;
• a doped region, which has been defined in the wide bandgap layer by doping part of the wide bandgap layer with a dopant that reaches the light-absorbing layer;
• and
• an electrode, which has been formed on the doped region,
• wherein a semiconductor multilayer structure, including the semiconductor conductive, light-absorbing and wide bandgap layers, has been formed on said surface region of the substrate, and
• wherein a second semiconductor conductive layer has been formed on another surface region of the substrate and is electrically isolated from the conductive layer included in the multilayer structure, and
• wherein a pad for use to electrically connect the photodetector to an external unit has been formed on the second conductive layer, and
• wherein the multilayer structure is covered with an insulating film, and
• wherein an interconnect has been formed on the insulating film to electrical connect the electrode and the pad together, and
• wherein the insulating film is a stack of an SiN layer and an SiO2 layer that has been deposited on the SiN layer.

A method for fabricating a photodetector, comprising the steps of:

• a) stacking semiconductor conductive, light-absorbing and wide bandgap layers in this order on a semi-insulating semiconductor substrate by a crystal growth process, wherein the conductive layer has etch susceptibility different from that of the substrate, the light-absorbing layer absorbs incoming light, and the wide bandgap layer has a bandgap wider than a bandgap of the light-absorbing layer;
• b) defining a doped region in part of the wide bandgap layer by doping said part with a dopant that reaches the light-absorbing layer;
• c) etching and patterning the wide bandgap and light-absorbing layers into respectively predetermined shapes;
• d) defining an etch mask on the conductive layer so that the wide bandgap and light-absorbing layers in the predetermined shapes are covered with the mask;
• and
• e) selectively removing part of the conductive layer using an etchant that etches said part of the conductive layer away with respect to the substrate.

A method for fabricating a photodetector, comprising the steps of:

• a) stacking semiconductor conductive, carrier barrier, light-absorbing and wide bandgap layers in this order on a semi-insulating semiconductor substrate by a crystal growth process, wherein the conductive layer has electrical conductivity, the barrier layer prevents carriers, created in the conductive layer, from diffusing and entering upper layers thereof, the light-absorbing layer absorbs incoming light, and the wide bandgap layer has a bandgap wider than a bandgap of the light-absorbing layer;
• b) defining a doped region in part of the wide bandgap layer by doping said part with a dopant that reaches the light-absorbing layer;
• c) defining a first etch mask on the wide bandgap layer so that the doped region is covered with the first mask;
• d) selectively etching part of the wide bandgap layer away with respect to the light-absorbing layer using a first etchant;
• e) defining a second etch mask on the light-absorbing layer so that the wide bandgap layer is covered with the second mask;
• f) selectively etching part of the light-absorbing layer away with respect to the barrier layer using a second etchant;
• g) selectively etching part of the barrier layer away with respect to the conductive layer using a third etchant;
• h) defining a third etch mask on the conductive layer so that the wide bandgap, light-absorbing and carrier barrier layers are covered with the third mask;
• and
• i) selectively etching part of the conductive layer away with respect to the substrate using a fourth etchant.

A method for fabricating a photodetector, comprising the steps of:

• a) stacking semiconductor conductive, light-absorbing and wide bandgap layers in this order on a semi-insulating semiconductor substrate by a crystal growth process, wherein the conductive layer has etch susceptibility different from that of the substrate, the light-absorbing layer absorbs incoming light, and the wide bandgap layer has a bandgap wider than a bandgap of the light-absorbing layer;
• b) defining a doped region in part of the wide bandgap layer by doping said part with a dopant that reaches the light-absorbing layer;
• c) etching and patterning the wide bandgap and light-absorbing layers into respectively predetermined shapes;
• d) selectively etching part of the conductive layer away, thereby defining a semiconductor multilayer structure, which includes the wide bandgap and light-absorbing layers in the predetermined shapes and the conductive layer, and leaving a second part of the conductive layer so that the second part serves as a second semiconductor conductive layer spaced apart from the conductive layer included in the multilayer structure;
• e) depositing SiN and SiO2 layers in this order over the surface of the multilayer structure, exposed parts of the substrate and the second conductive layer, thereby forming an insulating film including the SiN and SiO2 layers;
• f) removing part of the insulating film, which is located over the doped region in the wide bandgap layer included in the multilayer structure, thereby forming an opening over the doped region;
• g) forming an electrode on part of the doped region inside the opening;
• h) forming a pad for use to electrically connect the photodetector to an external unit on either part of the insulating film that has been formed on the exposed part of the substrate or another part of the insulating film that has been formed over the second conductive layer;
• and
• i) forming an interconnect on the insulating film to electrically connect the electrode and the pad together.