Fig. 1. (a) Cross-sectional scanning electron microscope (SEM) image of the optoelectronic upconversion device structure, including a red-emitting AlGaInP LED, a DBR, and a GaAs double-junction photodiode (DJPD), epitaxially grown on a GaAs substrate. The schematic of the corresponding circuit model is also shown, illustrating the upconversion mechanism. (b) Colorized SEM image (tilted view) of a fully fabricated device, showing designed LED (red color) and PD (gray color) components interconnected with metal wire (yellow color). (c) Top view, microscopic images of fabricated devices with different PD sizes (side length: 200 μm, 300 μm, 400 μm, 500 μm, 700 μm, 1000 μm, with a fixed LED size of 80 μm×80 μm) or LED sizes (side length: 80 μm, 150 μm, 200 μm, 250 μm, with a fixed PD size of 700 μm×700 μm) under the excitation of near-IR light (810 nm).

Fig. 2. (a) Measured TRPL decay curves for representative devices with different PD sizes (indicated in area) and a fixed LED size of 80 μm×80 μm. (b) Measured PL decay time as a function of PD size (red dots, with error bars included), in comparison with the theoretically calculated curve (blue dashed line). (c) Measured TRPL decay curves for representative devices with different LED sizes (indicated in area) and a fixed PD size of 700 μm×700 μm. (d) Measured PL decay time as a function of LED size (red dots, with error bars included), in comparison with the theoretically calculated curve (blue dashed line). For all curves, the maximum PL intensities are normalized to unity.

Fig. 3. (a) Microscopic image (top view) of an upconversion device emitting red light under near-IR illumination (LED size, 80 μm×80 μm; and PD size, 300 μm×300 μm). The green dashed square represents the edge of PD, and the white dots indicate the incident positions of focused IR laser spot. P1−P4 indicate four different incident points. (b) Measured TRPL decay curves of the upconversion device with different incident positions on the PD. (c) Measured PL decay time (red dots) as a function of the distance between the incident laser spot (P1−P4) and the nearest edge of the LED, in comparison with the theoretically calculated curve (blue dashed line).

Fig. 4. (a) Measured TRPL decay curves for a representative upconversion device (LED size, 80 μm×80 μm; PD size, 300 μm×300 μm) at different temperatures. (b) Measured PL decay time (red dots) as a function of temperature.

Fig. 5. (a) Schematic overview of representative upconversion mechanisms, including lanthanide-based, TTA-based, QD-QW-based, and our optoelectronic-device-based upconversion designs. (b) A summary of upconversion lifetimes and typical excitation power densities for four different mechanisms.

Fig. 6. Equivalent circuit of the IR-to-red optoelectronic upconversion device. The LED and DJPD are connected in series, and their capacitance and resistance render an RC delay.