Carrier Absence
Insulating regions within semiconductor p-n junctions lack mobile charge carriers due to internal electric fields. A formed depletion layer acts as the active sensing zone in photodiodes and radiation detectors. This region governs barrier potential, electric field distribution, and space charge limits within solid-state sensing components.
Boundary conditions define the depletion width based on dopant concentrations, stopping at the neutral bulk semiconductor regions where majority carriers predominate. Photons or ionizing particles entering this electric field generate electron-hole pairs that are immediately separated to create measurable photocurrent.
Junction Capacitance
The spatial width of the charge-free region dictates the internal junction capacitance of a sensor diode. A wider depletion layer reduces parasitic capacitance, increasing the response bandwidth of photodetectors. Physical layout parameters dictate baseline capacitive behavior.
Bias Dependence
Reverse bias voltage expands the internal carrier-depleted zone across the semiconductor junction. Applying reverse voltage increases depletion layer width, raising breakdown voltage limits and lowering transition capacitance. Excess reverse bias eventually leads to avalanche breakdown.
Sensing Mechanism
Absorbed radiation within the electric field region creates charge carriers that generate output signals. Electron-hole pair separation in the depletion layer occurs rapidly under strong drift forces, minimizing carrier recombination losses. Sensor sensitivity depends directly on matching the depletion region depth to the optical absorption length of incoming radiation.
