Homogeneous transparent conductive ZnO:Ga by ALD for large LED wafers

Highlights

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Highly conductive, transparent GZO layers were deposited by ALD.

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The ALD layers show superior thickness and sheet resistance homogeneity for 4” wafers.

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A two-step ALD deposition technique was proposed and demonstrated to improve the quality of GZO/p-GaN interface.

Abstract

Highly conductive and uniform Ga doped ZnO (GZO) films were prepared by atomic layer deposition (ALD) as transparent conductive layers for InGaN/GaN LEDs. The optimal Ga doping concentration was found to be 3 at%. Even for 4” wafers, the TCO layer shows excellent homogeneity of film resistivity (0.8 %) according to Eddy current and spectroscopic ellipsometry mapping. This makes ALD a favourable technique over concurrent methods like MBE and PLD where the up-scaling is problematic. In agreement with previous studies, it was found that by an annealing treatment the quality of the GZO/p-GaN interface can be improved, although it causes the degradation of TCO conductivity. Therefore, a two-step ALD deposition technique was proposed and demonstrated: a “buffer layer” deposited and annealed first was followed by a second deposition step to maintain the high conductivity of the top layer.

Keywords

• GZO; 
• Atomic layer deposition; 
• TCO; 
• Rapid thermal annealing; 
• LED
• • Source: Sciencedirect
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