Accurate Modeling for Small-Signal Response Analysis in GaInN/GaN-Based Micro-Light-Emitting Devices

Abstract

This study aimed to present an accurate model for small-signal response analysis that is universally applicable to GaInN/GaN-based micro-light-emitting devices (μ-LEDs) since the small-signal response analysis could lead to incorrect results when a conventional p–n (or p–i–n) junction (or depletion) theory is applied to the μ-LED structure as it is. To this end, an analytical model and an equivalent circuit were established, in which the additional undesired impact caused by the employment of the passivation layer was taken into account. To experimentally validate established models, two types of samples, i.e., ones with and others without a passivation layer, were fabricated from a single epitaxial wafer with varying chip sizes. The experimental results of impedance depicted that a metal–insulator–semiconductor capacitance (C_MIS) plays a significant role in the μ-LED structure in the aspect of small-signal response analysis, unlike that in the conventional structure. That is, the C_MIS should be considered and obtained separately. A methodology to obtain the C_MIS was suggested, which enables providing a reliable value of C_MIS in a simple way, thereby demonstrating junction capacitance, depletion width, doping profile, and built-in potential for μ-LEDs depending on the chip size. The experimental results showed that the methodology suggested in this study is very reliable. We firmly believe that the analytical model, the equivalent circuit, and the methodology presented in this study will shed light on further improvements in GaInN/GaN-based μ-LEDs.