Sep 6, 2016

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


•Highly conductive, transparent GZO layers were deposited by ALD.

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

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

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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