Sidewall passivation of Al_xGa_1−xAs homojunctions with wet chemicals and field-effect passivation by ALD oxides and nitrides

Reducing the sidewall recombination is of major importance for III-As p-n junctions especially for mesas with Perimeter/Area > 40 cm⁻¹. We investigated the sidewall passivation of two structures (GaAs and Al_0.1Ga_0.9As) with diameters down to 50 µm. The samples have been subjected to various wet chemical treatments prior to being coated with dielectrics. We studied the passivation properties of three oxides (Al₂O₃, HfO₂ and TiO₂) by thermal atomic layer deposition (ALD) and two nitrides (AlN and HfN) by remote plasma-enhanced ALD at 150 ^○C. We noted that a wet etch is required to remove damage from the dry-etched mesa surface. We found that Al₂O₃ with the metallic precursor as the first pulse provides the best ALD-based passivation and exhibits negative charges (Q_ox) above −4 × 10¹² cm⁻². Therefore, it performs as a field-effect passivation as confirmed by simulations. We quantified the passivation properties of the different dielectrics after encapsulation and annealing through the dark perimeter leakage, K_p02, for the different structures. HfN is a promising candidate with K_p02 of 1.2 × 10⁻¹² A cm⁻¹ and 2.1 × 10⁻¹³ A cm⁻¹ for GaAs and Al_0.1Ga_0.9As, respectively. To the best of our knowledge, this is the first ever reported study of HfN sidewall passivation.