Noise characteristics of lattice-matched InGaAs/InAlAs heterostructure p-i-n photodiodes

The authors report the experimental characterization of a set of three InGaAs/InAlAs heterostructure p-i-n photodiodes. Current-voltage, capacitance-voltage, S-parameter, and noise data were collected at room temperature over a wide range of bias current and voltage and a function of incident light intensity. The first device consisted of 360 alternating, undoped, lattice-matched In/sub 0.53/Ga/sub 0.47/As and In/sub 0.52/Al/sub 0.48/As layers 30 AA wide, sandwiched between an n/sup +/ and a p/sup +/ absorption layer of In/sub 0.53/Ga/sub 0.47/As. In the second and third device the number of layers and the layer width were respectively 200 and 90 AA and 50 and 500 AA. The capacitance-voltage data indicate that, in the dark, the heterostructure photodiodes are depleted gradually when the reverse bias is increased, i.e. one quantum well at a time. As a result, two high-field depleted regions at the contacts and a low-field undepleted region in the center are formed. Upon illumination by a light-emitting diode (1350 nm), the p-i-n photodiodes show large excess noise levels up to 500 MHz. Beyond this frequency the 30-AA devices show full short noise at field strengths E where impact ionization and Zener tunneling are absent, 0lt;E<220 kV/cm. The 90- and 500-AA devices, however, show distinctive subshot noise levels in the same field and frequency region. This difference in device operation can be understood in terms of the properties of the quantum-well structures located in the i-region of the device.