Distributed Bragg reflectors (DBRs) based on alternating layers of porous and non-porous GaN have been fabricated at the wafer-scale in heteroepitaxial GaN layers grown on silicon substrates. On the Si substrates a 250 nm-thick AlN nucleation layer, a 1700 nm graded AlGaN buffer (from 75 at% Al to 25 at% Al), and a 725 nm non-intentionally doped (NID) GaN buffer layer were grown by MOVPE. Onto this buffer, a 200 nm Si-doped (at 5 × 1018 cm-3) GaN layer was grown to provide a conductive pathway beneath the DBR. Next, a 200 nm NID GaN layer was added, followed by five periods of a latent DBR structure, each consisting of 58 nm highly Si-doped (at 1 × 1019 cm-3) GaN and 41 nm NID GaN. The 150 mm wafer was divided into (1.5 × 2.5) cm2 chips for porosification without lithographic processing. The porosification is achieved via electrochemical etching of highly Si-doped layers with 0.25 M solution of oxalic acid at etching voltages between 3V and 12V. Reflectance spectra were measured using a photoluminescence mapper with a broadband white light source. The measurements were normalised with respect to a pre-calibrated commercially available metallic mirror. Modelling of reflectance spectra was carried out using a transfer matrix model implemented in Microsoft Excel.

The following datasets have been deposited in this repository: Figure 3: (a) White light reflectance spectra for samples etched at voltages between 3 V and 12 V. Figure 3: (b) Peak reflectance values plotted against etching bias. Figure 6: Variation in porosity of the layer nearest to the surface with etching bias. Figure 7: (a) Predicted reflectance spectra for samples etched at between 3 V and 12 V, based on the porosity data in Figure 6.
Figure 7: (b) Predicted peak reflectance values based on the porosity data in Figure 6 plotted against etching bias. Figure S2: Simulated reflectance spectra for five pair GaN/porous-GaN DBRs with the porous layers having identical porosities between 20% and 70%.

Further details of the procedures and the datasets are described in the related publication.