Etchant for chemical thinning of InP and its application in the fabrication of InP diffused junction solar cells

A new etchant, which we have called ‘PNP’, with the composition ( o ‐H 3 PO 4 ) u : (HNO 3 ) v : (H 2 O)( 2 ) t : (H 2 O) 100−( u + v + t ) has been developed for thinning, after contacting, the n + and p + emitter layer of n + p and p + n InP structures made by thermal diffusion. By varying u , v and t , reproducible etch rates of 5–10 nm min −1 have been obtained. After thinning the 2.5–4.5 μm thick p + InP layer down to 60–250 nm, specular surfaces have been obtained at up to 80 nm min −1 etch rates. Owing to its intrinsic qualities, the residual phosphorus‐rich oxide after thinning the emitter layer provides surface passivation of p + InP surfaces and can also serve as a first‐layer antireflective coating. Very high quality p + n InP structures were also obtained using a thin (30–40 Å thick) phosphorus‐rich chemical oxide, grown using this etchant as a diffusion cap layer.