Simulation and Design of AlGaAs/InGaAs CCDs Based on pHEMT Technology

Abstract

Abstract-This paper describes the modeling, design and fabrication of quarter-micron double delta doped AlGaAs/InGaAs charge coupled devices whose epitaxial layers and geometry were based around the device structure of commercial pHEMTs. A quasi-two-dimensional physical model has been developed to investigate the properties of this novel 2 dimensional electron gas charge coupled device (2DEG-CCD). This physical model allows the characteristics of the InGaAs transport channel as well as the DC characteristics of the device to be predicted within a reasonable amount of time. This model also shows how 'individual' charge packets can be controllably transferred through the device when appropriate clocking voltages are applied to the gates of the CCD. This capacitive gate structure device is then shown to be successfully fabricated using established GaAs heterostructure fabrication techniques to ensure good repeatability. The DC characteristics of the fabricated charge coupled device delay line are included.Index Terms-2-DEG charge coupled devices, delay line, quasi-2d physical modeling, simulated charge transfer.

Simulation of Charge Transfer Process in a 2DEG-CCD

“…The length of the inter-electrode gap is 0.8 µm. Special care has to be taken when the length of the gate contacts is chosen, as this directly affects the time constants of the charge transfer mechanisms [6]. The GaAs transport layer is sandwiched between two doped (> 1018 cm-3) AlGaAs layers.…”

“…In this work, charge transfer process of a 2DEG-CCD by ensemble Monte Carlo method is simulated. In the simulation we used a simplified structure that reported in [6] with difference that a cermet film is used to encapsulate the inter-electrode gaps. The cermet film results in a monotonic variation of the surface potential between the electrodes at all clock frequencies [7].…”