THEORETICAL-STUDY OF POTENTIAL ULTRALOW NOISE, CONFINED STATE PHOTODETECTORS

A review of the basic issues implicit in the design of confined state photodetectors is presented. The basic device structure of a confined state photomultiplier consists of repeated unit cells each comprised o f a narrow-gap semiconductor layer sandwiched between barrier layers o f wider band-gap material. Gain in these structures is derived through carrier multiplication via impact excitation of confined electrons ou t of the narrow-gap semiconductor layer. Different device designs are considered in an attempt to maximize the device gain at minimum dark c urrent. In some implementations, the barrier layers are chosen to be g raded such that the leading edge discontinuity is at least twice that at the trailing edge of the well forming an asymmetric well design. We find that an asymmetric well design offers a much higher impact excit ation of electrons confined within the well at a lower operating volta ge than a symmetric well design, however, at the expense of increased dark current. Quantum versus classical confinement of the electrons wi thin the well is also investigated. Though the ionization rate within the classical confinement design is less under comparable conditions t o that in the quantum confinement design, the dark current is much les s within the classical structure than in the quantum structure, giving a higher excitation-rate-to-dark-current ratio. The gain and dark cur rent are investigated in structures made from GaN/AlGaN, HgTe/HgCdTe, and GaAs/AlGaAs.