Scaling of the structural characteristics of nanoholes created by local droplet etching

We study the tuneability of nanoholes created by local droplet etching of AlGaAs surfaces with Al droplets at varied coverage θ of the deposited droplet material and process temperature T. For the contact angle of the as-grown droplets a mean value of 66° is determined, which depends neither on θ nor on T. The experimental results on the hole structural characteristics are interpreted in terms of scaling models yielding a general form f (θ, T) θ q exp (E / [k B T]), with constants q and E and Boltzmanns constant k_B. In detail, the hole density varies from N 4.0 × 10⁶ up to 1.5 × 10⁸ cm^-2, and the scaling parameters are q 0 and E E_N 2.46 eV. The hole diameter varies from 50 up to 190 nm with scaling parameters q 1/3 and E -E _N/3. Moreover, the hole depth varies from 9 up to 125 nm with q 2/3 and E -1.73 eV. Furthermore, a threshold coverage of at least 0.2 monolayers (ML) must be deposited before hole formation takes place. In situ electron diffraction indicates that these 0.2 ML are consumed for a surface reconstruction change from (3 × 1) to (2 × 1). For coverages above 2.0 ML holes with a bimodal depth distribution are observed.