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UBC Theses and Dissertations

A single phase Al₀ 3Ga₀ 7As/GaAs heterojunction resistive-gate charge-coupled device Wohlmuth, Walter Anthony


The design, fabrication, and evaluation of a 128 pixel, single phase A10.3GavAs/GaAs heterojunction resistive-gate charge-coupled device (HRGCCD) is described. The HRGCCD has a higher operating speed and a larger charge handling capacity in comparison to the conventional buried channel, resistive-gate GaAs charge-coupled device (GaAs RGCCD). The higher operating speed of HRGCCDs is due to the higher electron mobility and velocity in an AlGaAs/GaAs heterojunction in contrast to a GaAs homojunction. In addition, the HRGCCDs can be integrated with high-speed on-chip high electron mobility transistors (HEMTs). The larger charge handling capacity of a HRGCCD is the direct result of the higher electron density in a HRGCCD in comparison to a GaAs RGCCD. A quantum mechanical model is used to calculate the carrier density in a triangular potential well formed at the interface between an undoped AlGaAs layer and an undoped GaAs layer. This model is coupled to a solution of Poisson's equation in bulk AlGaAs to determine the total carrier density in a HRGCCD for different layer and material specifications. This model is used to aid in the design of the HRGCCD. The fabrication of the HRGCCD required six mask levels employing 405 nm contact photolithography with a 1.0 µm design rule. Developments in the process technology previously employed at TRIUMF were required to create the HRGCCDs. These developments included a standard chlorobenzene-aided photoresist lift-off process to delineate r.f. magnetron sputtered Cr:SiO islands and a dry etch process to create interconnect vias. Two process runs of HRGCCDs, with differing layer parameters, were fabricated and evaluated at 4.33 MHz and at 50 MHz. The HRGCCDs tested at 50 MHz exhibited a charge transfer efficiency in excess of 0.99, and a dynamic range in excess of 50 dB with a linear response over a 40 dB input signal range.

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