4 research outputs found
Polarization-balanced design of AlN/GaN heterostructures: Application to double-barrier structures
Inversion- and depletion-regions generally form at the interfaces between
doped leads (cladding layers) and the active region of polar heterostructures
like AlN/GaN and other nitride compounds. The band bending in the depletion
region sets up a barrier which may seriously impede perpendicular electronic
transport. This may ruin the performance of devices such as quantum-cascade
lasers and resonant-tunneling diodes. Here we introduce the concepts of
polarization balance and polarization-balanced designs: A structure is
polarization balanced when the applied bias match the voltage drop arising from
spontaneous and piezeolectric fields. Devices designed to operate at this bias
have polarization-balanced designs. These concepts offer a systematic approach
to avoid the formation of depletion regions. As a test case, we consider the
design of AlN/GaN double barrier structures with
AlGaN leads. To guide our efforts, we derive a
simple relation between the intrinsic voltage drop arising from polar effects,
average alloy composition of the active region, and the alloy concentration of
the leads. Polarization-balanced designs secure good filling of the ground
state for unbiased structures, while for biased structures with efficient
emptying of the active structure it removes the depletion barriers
Temperature stability of intersubband transitions in AlN/GaN quantum wells
Temperature dependence of intersubband transitions in AlN/GaN multiple
quantum wells grown with molecular beam epitaxy is investigated both by
absorption studies at different temperatures and modeling of conduction-band
electrons. For the absorption study, the sample is heated in increments up to
C. The self-consistent Schr\"odinger-Poisson modeling includes
temperature effects of the band-gap and the influence of thermal expansion on
the piezoelectric field. We find that the intersubband absorption energy
decreases only by meV at C relative to its room temperature
value