研究目的
To understand the effect of the strain originating from two different sapphire substrates on the performance of InGaN blue light-emitting diodes (LEDs).
研究成果
The study concludes that the trap densities of InGaN LEDs grown on different substrates are slightly different, but the trap lifetime of the PSS is about six times longer than that of the CSS. The trap levels of the CSSs are located at energy levels that are 50 meV shallower relative to those of the PSSs, attributed to the stronger piezo-field in CSSs. This difference in carrier trapping times affects the luminescence efficiencies of the InGaN QWs in the two devices.
研究不足
The study focuses on the effect of strain on the performance of InGaN blue LEDs grown on different substrates but does not explore other potential factors that could influence LED performance. The comparison is limited to two types of substrates, and the findings may not be generalizable to other substrate types or LED configurations.
1：Experimental Design and Method Selection:
The study compares two types of blue InGaN LEDs grown on patterned sapphire substrates (PSS) and conventional sapphire substrates (CSS) to understand the effect of strain. Methods include time-resolved photoluminescence (TRPL), electroreflectance (ER), and dynamic capacitance dispersion measurements.
2：Sample Selection and Data Sources:
InGaN-based blue LEDs were grown on PSS and CSS. The samples were prepared using metal-organic chemical-vapor deposition.
3：List of Experimental Equipment and Materials:
A 405-nm wavelength InGaN pump laser diode for TRPL measurements, equipment for ER spectroscopy, and dynamic capacitance measurement setup.
4：Experimental Procedures and Operational Workflow:
The study involved measuring the light-current output power (L-I) and external quantum efficiency (EQE) curves, TRPL intensities, ER spectra under reverse bias voltages, and dynamic capacitance with frequency dispersions.
5：Data Analysis Methods:
Analysis included calculating the internal field in the InGaN QWs from the flat-band voltage, estimating trap density and trap characteristic time, and deriving trap state energy from the conduction band edge.
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