Pyramid Formation by Etching of InxGa1−xN/GaN Quantum Well Structures Grown on N‐face GaN for Nanooptical Light Emitters

Abstract

Nanooptical light emitters based on semiconductors are very promising for a broad range of applications such as single-photon sources or optical sensors of nanoobjects. The group-III nitrides are especially interesting in this respect as light emitters in the visible range with high efficiency are nowadays commercially available. By changing the indium content, the bandgap of In x Ga 1Àx N can in principle be tuned over the whole wavelength range from the near-IR region to the near-UV region. In most studies, three routes are followed to produce nanooptical light emitters: 1) the self-assembled growth of quantum dots (QDs), [1,2] 2) the growth of pyramids by applying masks of, for example, SiO 2 , [3] or 3) the growth [4,5] or topÀdown fabrication [6] of nanorods. The first one suffers from the high defect density in group-III nitride growth when using conventional sapphire, SiC, or silicon substrates, [7] that the sites of the QDs are unknown (unless further steps are taken), the properties are critically dependent on the growth conditions, and that it is difficult to stabilize the QDs in further growth. The second one has the problem that indium incorporation on different parts of the pyramid, side facets, edges, and tip, varies and is difficult to control, which typically result in an inhomogeneous emission. Furthermore, defects may form, induced by the mask, which reduce the efficiency. The insertion of QDs in nanorods during growth shows, up to now, low efficiency. A topÀdown approach to realize QDs in etched nanorods would be quite a challenge due to the length of the nanorods and the small required diameters.Hence, for the generation of a large array of as similar as possible nanooptical light emitters, we propose another solution. A single or multiquantum well (SQW, MQW) structure is grown on N-face GaN and in a second step pyramids are formed by wet chemical etching. This has the advantage that the QW can be optimized independently of pyramid formation. However, in contrast to the N face, the Ga face is chemically inert and plasma etching processes may create damage, which reduces the efficiency. Another advantage of using N-face GaN is that the