Ultra-small micro-LEDs are essential for next-generation display technology. However, micro-LEDs below 5 μm have been seldom reported. In this work, we demonstrate InGaN-based blue and green micro-LEDs from 1 to 20 μm by using laser direct writing lithography. The 1-μm blue micro-LEDs show a peak external quantum efficiency of 13.02%, which is 9.57% for green ones. By characterizing the size-dependent external quantum efficiency and simply assuming that this variety is dominantly determined by the dry-etching induced dead zone, we deduce that the dead zone sizes of carrier injection at the edge of chips are 0.18 and 0.15 μm in blue and green ones, respectively. A time-resolved photoluminescence measurement also shows that carrier lifetime reduction at the edge of blue ones is more serious than that of green ones, reflecting the easier carrier lateral diffusion in the former than the latter. These results exhibit the ability of laser direct writing lithography on micro-LED fabrication and also provide a reference for predicting the limit of their chip size scaling-down.

In this paper, the optical properties of GaN-based green light emitting diode (LED) are investigated and the internal quantum efficiency (IQE) values are measured by temperature dependent photoluminescence (TDPL) and power dependent photoluminescence (PDPL) methods. The "S-shaped” shift of peak wavelength measured at different temperature disappears gradually and the spectra broadening can be observed with increasing excitation power. The IQE calculation results of TDPL, which use the integrated intensity measured at low temperature as unity, can be modified by PDPL in order to acquire more accurate IQE values.

Carrier escape has been widely observed in light-emitting diodes (LEDs) and it is crucial to the performance of quantum-well photovoltaic and photodetector devices. However, the mechanisms proposed thus far, including thermionic emission and direct tunneling, fail to explain the experimental results. In this work, a simplified trap-assisted tunneling model that considers the energy distribution on trap states is established through which experiment results can be explained reasonably. The nonuniform distribution of diffused p-type dopants is proposed as the reason for the abnormal voltage-dependent and excitation-energy-dependent photocurrent experimental results through energy band diagram simulation.

The processes of carrier escape and injection in InGaN/GaN LEDs have been studied separately and the underlying correlation between these two processes has been overlooked for a long time. In this study, the behavior of photogenerated carriers in LEDs is discussed which shows that the process of carrier escape and injection share the same transport channel. It is further confirmed by comparing the forward voltage under electrical excitation and open-circuit voltage under photo-excitation with the same luminous intensity. These results will not only deepen our understanding of device physics but also guide the design of devices used for display and detection.