| Monolithically integrated photoreceivers, optoelectronic integrated circuit photoreceivers (OEIC), are important components for fiber optic communications. Two novel delta modulation doped HMSM photodetectors with resonant cavities have been designed with improved performance in terms of responsivity, speed, sensitivity, and wavelength selectivity to fulfill the increasingly more stringent requirements of transmission systems. The major contributions of the author during the Ph.D. period are as follows: (1) A closed-form model was developed to describe the electronic properties of delta modulation doped heterostructures, which has been compared with a modified self-consistent method of solving Schrödinger and Poisson equations. (2) A GaAs based and an InP based delta modulation doped HMSM photodetectors with a resonant cavity have been designed for short haul and long haul optical communications, respectively. (3) Two different groups of GaAs based devices with various geometries have been fabricated and characterized: one with the delta modulation doped structure, the other without this doping. Delta doped photodetector shows wavelength selectivity at 850 nm, with 9.2 fA/μm2 dark current, 0.08 A/W average photo responsivity, less than 30 fF capacitance, 10.6 ps full width at half maximum, 9 ps rise time, and 18.4 ps fall time. (4) The most important feature of the delta doped GaAs based device is its improvement of the optical and speed response: its dc photocurrent increases by a factor of 1.6 while the dark current reduces by a factor of 7.8 under 4V bias and a 7 GHz expansion of the 3dB bandwidth under 5V bias compared to the undoped device. The mechanism responsible for the reduction of dark current is enhancement of the cathode metal-semiconductor barrier due to the confined electron cloud, as well as band bending in the anode that reduces hole current flow. The increase in responsivity and speed of response is attributed to the vertical electric field and suitable potential profile in the direction of growth. The device designed, analyzed, characterized, and presented here is an excellent candidate for optical detection purpose, especially for fiber optic communications. |
