InP Quantum Dot Intermediate Band Solar Cell Grown via MOCVD

Growth of type-II InP quantum dots in wide bandgap InGaP (EG = 1.85 eV) for intermediate band solar cell applications is studied, grown via Aixtron close-coupled showerhead metal-organic chemical vapor deposition system. Theoretical calculation and optical characterizations verify type-II band alignment, showing approximately 300 meV electron confinement in the conduction band and around 5 meV potential barrier for holes in the valence band. AFM measurements predominantly show type-II dots (dot height greater than 15 nm), which is further verified by a single QD peak with narrow full width at half maximum obtained by photoluminescence measurements. Dot density of 0.7 × 10
¹⁰
cm
^-2
is measured with diameter and height of 56 ± 10 nm and 18 ± 2.8 nm, respectively. This quantum dot system promises a more ideal band alignment for intermediate band assisted photon absorption and higher two-step photon absorption (TSPA) temperatures. Here, we observe TSPA response up to 200 K for a solar cell with 5x layers of InP QDs in the intrinsic region.