Project

This workpackge deals with the fine-optimization of the chemical beam epitaxy and characterization of the Ga(As,P), Ga(P,N) and Ga(As,N) alloys that will be used later on for the fabrication of the short-period superlattices. Hence, we will fabricate these materials first as thin layers with the chemical compositions derived from the studies performed in WP1. Nevertheless, we will not wait until obtaining all results from WP1 to gain control on the chemical composition of the different alloys since the range of interest is already known from C. Macías Diaz’s Mastet thesis. We will synthesized both undoped and doped layers to have a reference for the subsequent n- and p-type doping of short-period superlattices. In addition, we will also fabricate Ga(As,P,N) layers to compare, at a later stage, the properties on the same materials grown as thin films and superlattices. Since it is known that the optical properties of diluted nitrides improved after they are annealed at elevated temperatures (> 700 °C), we will additionally analyze the impact of rapid thermal annealing processes on the properties of our layers. All samples will be grown on commercial GaP on Si(001) substrates. Despite a 300 mm GaP on Si wafer costs 8500 €, for research purposes, the final quality of the obtained materials and the enormous save on time and efforts, comfortably compensate for the extra cost in comparison to bare Si wafers. Moreover, since 300 mm wafers will be diced in about 175 pieces with an area of 2 × 2 cm2, the substrate cost per experiment will be very reasonable, namely, less than 50 €. Importantly, we stress that the high cost of these wafers does not imply a high cost for a future commercial production of the double-junction solar cells that motivate this project because of the technological steps required for the fabrication of GaP on Si are: (i) well reported in the literature and (ii) the cost for the fabrication of such a buffer layer is absolutely negligible when taking into account to total costs of the entire III-V epitaxial process, which must be carried in the same epitaxial reactor. The elevated cost of commercial GaP on Si substrates is due the lack of competitors in the market, so far these substrates are exclusively commercialized by the company
NAsP III-V. Upon the growth, the chemical composition, structural, morphological, optical and electrical properties of the samples will be analyzed by using a wide variety of experimental techniques including: High-resolution X-ray diffraction (HR-XRD), Rutherford backscattering spectrometry (RBS), nuclear reaction analysis (NRA), atomic force microscopy (AFM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), photoluminescence spectroscopy (PL), photoreflectance spectroscopy (PR), cathodoluminescence spectroscopy (CL), spectroscopic ellipsometry (SE), Hall-profiling, C-V and I-V measurements.