A precise method for stacking semiconductor
thin films enhances optoelectronic device performance using quantum effects.
A method to
nanoengineer an emerging family of semiconductors known as perovskites could
reduce the cost of high-performance optoelectronic devices.
The properties of a
semiconductor can be controlled by nanoscale engineering using technologies
that slowly deposit atoms on a substrate. These methods are expensive and
limited to conventional semiconductor materials, motivating scientists to
search for new methods.
Quantum wells are
semiconductor films of just a few nanometers, sandwiched between two thicker
layers of a different semiconducting material. An energy barrier between the
two materials blocks the electrical charge carriers from leaving the well
layer, effectively limiting their motion to two dimensions. This radically
alters the well material’s properties, making them more optically active, for
example. This effect can be amplified further by combining multiple quantum
wells into a single stack.
methods—depositing crystalline film on a crystalline substrate—are used to
construct such stacks from gallium arsenide or gallium nitride by expensive
processes with specialized equipment. But, another more practical approach is
needed if this multiple quantum well architecture is to be used in perovskite
devices. “Metal halide perovskites have excellent energy conversion efficiency
for light harvesting and photoluminescence,” says postdoc Kwang Jae Lee from
Osman Bakr’s Lab in the KAUST Catalyst Center. Quantum wells could
improve this efficiency still further.
colleagues from across KAUST and in collaboration with researchers from Korea,
Bakr, Lee and team created perovskite multiple quantum wells using a simple
technique known as thermal evaporation. They started with powders of their
chosen perovskite well material, CsPbBr3, and a barrier
material, TPBi. These powders evaporated when heated in a vacuum chamber, and
the vapor particles traveled to a substrate where they formed a film. The team
alternated between heating the TPBi and the CsPbBr3 to make their quantum wells.
Key to their success
was calibration of the deposition rate. The team optimized the evaporation
rates of their CsPbBr3 and TPBi powders at 0.015 and 0.020
nanometers per second, respectively. Unlike most epitaxial technologies,
thermal evaporators are simple and widely available. Moreover, epitaxial
methods need a substrate with a similar atomic lattice spacing to that of the
deposited layer. The evaporation method, however, is applicable to any
substrate; Lee and the team used simple glass because of the defect tolerance
of perovskite materials.
think this is just the beginning,” says Lee. “The study points in one unexplored
direction in perovskite research, and we expect further exciting perovskite
devices based on this work in the near future.”
- Perovskite-based artificial multiple quantum wells. Nano Letters 6, 3535-3542 (2019).
Lee, K. J, Turedi, B.,
Sinatra, L., Zhumekenov, A. A. Maity, P. Dursun, I., Naphade, R.,
Merdad, N., Alsalloum, A., Oh, S., Wehbe, N., Hedhill, M., Kang, C.H.,
Subedi, R.C., Cho, N., Kim, J.S., Ooi, B., Mohammed, O.F. & Bakr,
Sandra Ramirez Cherbuy