In some embodiments, a semiconductor structure includes a first conductivity type region comprising a first superlattice, and an i-type active region adjacent to the first conductivity type region comprising an i-type superlattice. The first conductivity type region can be a p-type region or an n-type region. The first superlattice can be comprised of a plurality of first unit cells comprising a first set of single crystal layers, and the i-type superlattice can be comprised of a plurality of i-type unit cells comprising a second set of single crystal layers. An average alloy content of the plurality of the first unit cells and the i-type unit cells can be constant along a growth direction. A combined thickness of the second set single crystal layers can be thicker than a combined thickness of the first set of single crystal layers.