The recently proposed diffusion-driven charge transport (DDCT) method can allow a paradigm shift in the design of optoelectronic devices, by changing both the current injection principle and the device structure. The DDCT injection technique is based on the bipolar electron and hole diffusion currents that are used to electrically inject charge carriers into an active region (AR) located outside the p-n junction. In this article, we study an interdigitated back-contacted DDCT-light-emitting diode (LED) based on a GaInP/GaAs double heterojunction (DHJ) structure consisting of lateral heterojunctions (LHJs) located above a uniform AR. The structure uses single-sided electrical injection and is suitable for large-area applications and thin-film devices with near-surface ARs. Our analysis, based on charge transport simulations, suggests that the structure permits more efficient current spreading and lower surface recombination than conventional structures, leading to a very high internal quantum efficiency (IQE) and injection efficiency exceeding 99%. Particularly, we investigate the implications of using the new structure for improving the efficiency of LEDs, bringing them closer to the threshold of electroluminescent cooling (ELC). The results predict an above-unity internal power conversion efficiency for the DDCT-LEDs, substantially exceeding the efficiency of conventional reference devices, highlighting the new possibilities that DDCT devices offer especially for high-power ELC at room temperature.
Interdigitated back‐contact (IBC) silicon solar cells are coming of age, but the potential of IBC configurations for compound semiconductor solar cells is yet to be explored. We outline an approach to generalize the diffusion‐driven charge transport (DDCT) method, previously studied for IBC light‐emitting diodes, to develop DDCT solar cells, enabling an IBC double‐heterojunction structure. In particular, we simulate and compare the electrical performance of a GaInP/GaAs DDCT solar cell with an ideal one‐dimensional reference cell to establish how the lateral dimensions of the DDCT structures affect their operation. Also, the suitability of the DDCT solar cells for concentration photovoltaics is explored. The results show that the DDCT solar cells with a finger pitch of approximately 10μm can match and even outperform the ideal reference structure under the AM1.5G solar spectrum, due to reduced Shockley‐Read‐Hall recombination. At high solar concentrations, the performance of the smallest pitch DDCT structure is essentially identical with the reference structure up to 100 suns. This suggests that combining the benefits offered by the IBC design with compound semiconductors could allow the development of an entire family of more efficient solar cells.
Diffusion-driven charge transport (DDCT) in III-V light-emitting diodes (LEDs) can enable unconventional optoelectronic devices and functionality by fundamentally changing device design and the current injection principle. In our recent study, an AlGaAs/GaAs DDCT-LED consisting of an array of lateral heterojunctions was studied for large-area applications at high powers. Here, we investigate the current spreading and recombination uniformity of a modulation doped GaInP/GaAs DDCT-LED. In particular, we analyze how the background doping of the lower GaInP cladding layer (CL) and the GaAs substrate changes the carrier distribution within the active region of the device. Our charge transport simulations based on the drift-diffusion current and continuity equations predict that modulation doping by a p-doped CL provides much higher recombination uniformity at high powers compared to an n-doped CL. Most importantly, improved current spreading is achieved while maintaining excellent device performance.
Compound semiconductor devices utilizing interdigitated back-contact (IBC) designs with a uniform active region (AR) can enable a new generation of optoelectronic devices with eliminated contact shading, reduced resistive losses, and minimal current crowding. However, appropriate lateral doping techniques for such devices are not yet established. This work demonstrates selective-area diffusion doping from an epitaxially grown dopant source layer enabling the fabrication of GaAs-based light-emitting diodes (LEDs) utilizing diffusion-driven charge transport (DDCT) and the IBC design. The effects of doping and device dimensions are analyzed by comparing current-voltage characteristics and electroluminescence (EL) of laterally doped DDCT structures and control structures with several characteristic finger widths between 15 and 300 µm. Additional simulations confirm that the DDCT structure enables effective carrier injection into a buried AR outside the p-n junction. A current density of 1.25 A/cm 2 was measured for the fabricated DDCT-LED with 15-µm wide fingers at a moderate bias voltage of 1.3 V. The light emission from the DDCT-LEDs shows clear signs of lateral current injection, improved current spreading, and a tenfold increase in EL, when compared to control structures specifically designed to validate the presence of diffusion doping. These results indicate that diffusion doping can enable the means to fabricate DDCT structures with effective carrier injection into a uniform AR.
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