Single-Layer InAs Quantum Dots for High-Performance Planar Photodetectors Near 1.3 $\mu\hbox {m}$

The potential of InAs quantum-dot (QD) photodetectors for room-temperature high-speed operation at wavelengths near 1.3 μm is evaluated. Specifically, planar metal-semiconductor-metal structures on GaAs substrates containing one absorption layer of self-assembled InAs QDs embedded in Ga(In)As matrices are fabricated, characterized, and analyzed. Light absorption, optically generated carrier transport, and collection mechanisms are studied. The role of the QD embedding matrix in the lateral transport of the photogenerated carriers is also studied by comparing structures with QDs in GaAs and In_0.15Ga_0.85As matrices. Devices show low dark currents in tens of nanoamperes and high light sensitivity when adjusted to QD volumes, whereas external quantum efficiency remains in the range 10^-5-10^-4 for all fabricated samples. The time response of the fabricated devices is obtained using an excitation wavelength resonant with QD interband transitions, thus allowing the photogeneration of electron-hole pairs inside the dots. Results prove detection capability of a single layer of QDs in a common photodetector structure with a full-width half-maximum time response on the order of 10 ps. A long tail, about 100 ps, but at a small fraction of the peak response amplitude, is also observed, suggesting mechanisms for charge transport and collection.