The work describes multiband photon detectors based on
semiconductor micro- and nano-structures. The devices considered
include quantum dot, homojunction, and heterojunction structures.
In the quantum dot structures, transitions are from one state to
another, while free carrier absorption and internal photoemission
play the dominant role in homo or heterojunction detectors.
Quantum Dots-in-a-Well (DWELL) detectors can tailor the response
wavelength by varying the size of the well. A tunneling Quantum
Dot Infrared Photodetector (T-QDIP) could operate at room
temperature by blocking the dark current except in the case of
resonance. Photoexcited carriers are selectively collected from
InGaAs quantum dots by resonant tunneling, while the dark current
is blocked by AlGaAs/InGaAs tunneling barriers placed in the
structure. A two-color infrared detector with photoresponse peaks
at ~6 and ~17 μm at room temperature will be
discussed. A Homojunction or HEterojunction Interfacial
Workfunction Internal Photoemission (HIWIP or HEIWIP) infrared
detector, formed by a doped emitter layer, and an intrinsic layer
acting as the barrier followed by another highly doped contact
layer, can detect near infrared (NIR) photons due to interband
transitions and mid/far infrared (MIR/FIR) radiation due to
intraband transitions. The threshold wavelength of the interband
response depends on the band gap of the barrier material, and the
MIR/FIR response due to intraband transitions can be tailored by
adjusting the band offset between the emitter and the barrier.
GaAs/AlGaAs will provide NIR and MIR/FIR dual band response, and
with GaN/AlGaN structures the detection capability can be extended
into the ultraviolet region. These detectors are useful in
numerous applications such as environmental monitoring, medical
diagnosis, battlefield-imaging, space astronomy applications, mine
detection, and remote-sensing.