Title

Infrared Photodetection and Related Studies in a Modulation-Doped Heterostructure

Date of Completion

January 2011

Keywords

Engineering, Electronics and Electrical

Degree

Ph.D.

Abstract

The device model of the modulation doped heterostructure is established in Agilent advanced design system (ADS). The model is now considered complete with the inclusion of change of carrier density as a function of time and the proper representation of photocurrent. ^ The bipolar inversion channel field effect transistor (BICFET) gains of 20–40 are observed with BVeco=8 V and offset Vec=0.2 V. A 1 × 100 µm 2 heterostructure field effect transistor (HFET) shows a transconductance of 162 ms/mm. The mechanism of low current gain of the BICFET is attributed to the diffusion current from the emitter to the base. ^ Infrared (IR) photodetection capability of the heterostructure is demonstrated by the intersubband absorption between the first subband in the quantum well and the bottom of the continuum in the charge sheet. An absorption coefficient of 1000–1700 cm−1 was observed in both n- type and p- type structure over a range of wavelength of 8–12 µm. An analytical model based upon reduced mass and relaxed k conservation was established. The characteristics of a thyristor photodetector including detectivity, quantum efficiency and photo current were determined. ^ The optoelectronic integrated circuits (OEICs) capability of the heterostructure is demonstrated through experiments. Both lateral in-plane waveguide coupling and direct coupling through the edge of the waveguide are tested at 980 nm wavelength. A responsivity of 0.3 A/W is estimated. The dependence of change of barrier voltage on the injected light is modeled. ^ A big loss in the waveguide is found due to the passive waveguide absorption. Methods of quantum well intermixing (QWI) are studied and impurity free vacancy disordering (IFVD) is chosen as the solution. Experiments show that the implantation of n- type species and deposition of a 1000–1500 Å dielectric layer are effective. A blue shift around 90 nm is observed. Different conversion doping, thermal treatment and thickness of the dielectric layer have been tested to show the relevance to the band gap widening. ^ The disk photoreceiver model is discussed to implement wavelength division multiplexing (WDM). Sub-picojoule-per-bit operation at 10 Gb/s is achieved through simulation. The quality factor of 1700 is obtained in the model. ^

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