South Korea study confirmed: trench filling P type gallium nitride InGaN can increase the output power of LED

Seoul National University and Samsung Electronics Co Ltd have been filled with trench P type gallium nitride to increase the output power of InGaN LED.

The purpose is to make the hole groove more effectively into the multi quantum well (MQW) structure. In traditional LED, from the top of the p-GaN contact layer holes tend to be away from the well top, which means that the light emitted from the lower part of the trap is not too much. The number of grooves, the researchers hope to increase equipment into the deep part of the hole (Figure 1a).

Figure 1. (a) MQW hole of conventional LED and P type groove, the distribution of LED (b) or tension is eliminated, the band structures of MQW

The researchers also want to use split groove material can reduce the pressure strain electric field in MQW structure caused by III nitride polarization. The tension is due to the emergence of GaN and InGaN between the structure of crystal lattice mismatch.

In the quantum well structure, the internal polarization electric field, the band is inclined, the electron and hole separation, wave function overlap decreased, and converted into photons (Figure 1b), which is usually called quantum confined Stark effect (QCSE). The growth of material in the semi polar or non-polar crystal orientation can avoid this effect, but the GaN substrate usually requires the use of expensive self-supporting or large.

The hole transport leads to high current injection is one reason for the low efficiency. Because most of the electron hole recombination occurred in one or two wells, the starting current will be "non radiative auger" like reducing. In addition, the probability of electron overflow to p-GaN contact layer is greatly increased.

Using metal organic chemical vapor deposition (MOCVD) of 3nm/12nm InGaN / GaN MQWs grown on C sapphire substrates by electron beam lithography, trench definition. The active region of a blue light. Lithography (PMMA) 100nm in PMMA resist coating on. Will form a pattern of transfer to the MQW structure by inductively coupled plasma etching, at the temperature of 950 DEG C and under the pressure of 200Torr, the lateral growth of P type GaN trench filling.

The researchers also tried a selective wet etching method using potassium hydroxide at 165 DEG C in ethylene glycol to form a trench, by adding indium tin oxide (ITO) to test the current diffusion layer structure of electroluminescence. The metal contact points for chromium / nickel.

Researchers estimate that the light output power equipment discharge no groove is about 5% with similar active region LED. Create a trench increase light output by dry etching, and blue transfer with shorter wavelengths (Figure 2).

Figure 2. (a) optical output power P groove structure using electron beam lithography and conventional structure; (b) electroluminescence (EL); and (c) the forward and reverse current (D).

1 m trench maximum light output. The researchers commented: "this is because the P groove structure also reduces the volume of MQW, while reducing the tension and QCSE. Therefore, in order to maximize the output power, it is important to optimize the ratio between the volume and the remaining groove structure of the MQW volume."

The wavelength shift in 500nm - from the largest trench 431nm to 420nm, so the effective band gap increases from 2.76eV to 2.85eV, this is due to the relaxation of tension. P channel increases the forward current for a given voltage, and the leakage increase under reverse bias.

Wet etching groove also increases the light output power, but did not significantly increase. In addition, the technology is not very effective in the relaxation of tension. The current voltage behavior is also affected by the impact of small wet etching groove. (compiled: LED James)

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