COMPARISON BETWEEN GALLIUM-IMPLANTED LAYERS OF ZNSE AND ZNSXSE1-X BY OPTICAL, ELECTRICAL AND ELECTRON-BEAM CHARACTERIZATION METHODS

Optoelectronic devices in the blue spectral region require doped ZnSxS e1-x layers for electrical confinement and optical waveguiding. Since ion implantation is often used to realize heavy doping in thin layers, we implanted gallium ions with different doses and energies into ZnSe and ZnSxSe1-x (x less-than-or-equal-to 0.4) layers, grown by metalorg anic vapor phase epitaxy (MOVPE) on GaAs. Rapid thermal annealing was performed after SiO2 capping. For characterization, we used electron p robe micro-analysis (EPMA), photoluminescence (PL) at 11 K, Raman spec troscopy, far infrared reflectivity (FIR) and Hall measurements. In Zn Se, the Ga depth profiles remain nearly gaussian after annealing, indi cating weak diffusion. PL shows that both the overall intensity and th e ratio of excitonic to deep centre emissions are maximum for annealin g at 850-degrees-C (30 s), implying optimum crystalline quality and ma ximum carrier concentration. In addition, the conductivity is maximum (10 OMEGA-1 cm-1). However, FIR reveals a heavily doped layer at the G aAs interface, which is assigned to the annealing-induced Zn diffusion into the substrate. Furthermore, the PL spectra show donor-acceptor p air (DAP) transitions which can be attributed to shallow acceptors due to complexes of Ga and intrinsic defects. With increasing ion dose th e free carrier concentration saturates at 4 X 10(17) cm-3 probably due to self-compensation caused by zinc vacancies (VZn). For ZnS0.3Se0.7, EPMA measurements show a diffusion of the Ga towards the surface, whi le S- and Ga-rich surface defects appear during annealing. After impla ntation the PL spectra show deep level emissions at 2.08 and 2.35 eV, which were assigned to [Ga(Zn)-V(Zn)] complexes and to Zn(Se). Optimum annealing seems to occur at 850-degrees-C for 30 s, resulting in a ma ximum PL intensity with strong DAP and excitonic contributions. Simila r behaviour was observed for ZnS0.4Se0.6. Up to now, due to the diffus ion and compensation, the implanted and annealed ternary layers remain semi-insulating.