263III-Nitride Semiconductors: New Infrared Intersubband Technologies
diagram of a step-QW design, in this example consisting of Al
0.1
Ga
0.9
N/GaN/
Al
0.05
Ga
0.95
N (3 nm/3 nm/10 nm). This three-layer structure is designed around the
principle of polarization equivalency. The design can be broken effectively into two
portions: The rst is the “barrier,” which comprises the high-Al-content Al
x
Ga
1 – x
N
layer and the GaN layer. The second portion is the “well,” which is the low-Al-
content Al
x
Ga
1 – x
N layer. The design creates a semi-at band in the well by having
the barrier balanced at the same average Al percentage, that is, the average polariza-
tion in the barrier is approximately equal to the average polarization in the well. This
conguration is ...