Growth and Characterization of Ga(As,N) and (In,Ga)(As,N)

This dissertation deals with the MBE growth and characterization of Ga(As,N) and (In,Ga)(As,N). The work commences with the optimization of the Ga(As,N) growth. Owing to a large miscibility gap of GaN in GaAs, the substrate temperature is the most crucial growth parameter. We will show that growing Ga(As,N) at high substrate temperatures leads to a roughening of surfaces and interfaces. Low substrate temperatures are therefore mandatory to warrant the morphological quality of Ga(As,N). The parameters of the nitrogen plasma source have an important impact upon the optical properties of Ga(As,N). We will demonstrate that a lowering of the plasma source power and nitrogen flow yields an improvement of optical properties, namely an increase of the photoluminescence intensity and a decrease of the halfwidths of the photoluminescence spectra. Another topic of this work will be the investigation of surface and interface roughening of Ga(As,N) with respect to the nitrogen concentration and the quantum well thickness. Experimental results will be presented that show a clear transition from smooth to rough surfaces and interfaces if a certain Ga(As,N) roughening thickness is exceeded. We will demonstrate that rough Ga(As,N) samples show regions of higher nitrogen concentrations within the Ga(As,N) quantum wells, whereas no misfit dislocations are detected. Owing to low substrate temperatures and the use of a nitrogen plasma source, point defects are inevitable in the Ga(As,N) material system. A thermal treatment of Ga(As,N) reduces the concentration of these point defects. This leads to a substantial improvement of optical properties. We will show that nitrogen split interstitials that incorporate into gallium and arsenic vacancies may be attributed to these point defects. Growing Ga(As,N) in an external magnetic field also causes an improvement of optical properties. This observation will be elucidated by the existence of ions generated by the nitrogen plasma source. We will also present experimental evidence that a thermal treatment of Ga(As,N) leaves the nitrogen concentration profile almost unchanged. A thermal treatment of Ga(As,N) at high temperatures results in a creation of extended defects which are detrimental to optical properties. We will show that the temperature of the thermal treatment that yields the highest photoluminescence intensity is nitrogen concentration-dependent. Investigations on radiative recombination in Ga(As,N) will be performed. We will provide experimental evidence of localized excitons, either trapped in potential fluctuations or defects. An increase of the excitation density and/or the temperature causes a transition from localized to delocalized excitons. A thermal treatment of Ga(As,N) reduces the concentration of these defects. Still, for healed out Ga(As,N) samples, excitons are localized in potential fluctuations. An estimate of the potential fluctuation concentration in dilute Ga(As,N) will be drawn. We will demonstrate that the growth of (In,Ga)(As,N) is similar with respect to Ga(As,N). Again, one has to face a high miscibility gap of (In,Ga)N in (In,Ga)As. Consequently, low substrate temperatures are mandatory to ensure smooth surfaces and interfaces of the quaternary material system. A thermal treatment of (In,Ga)(As,N) is also beneficial for improving optical properties. We will show that a thermal treatment of (In,Ga)As results in an indium interdiffusion that is suppressed by the incorporation of nitrogen. We will explain this observation with an incorporation of nitrogen into gallium vacancies. (In,Ga)As edge emitting lasers with indium concentrations between 13 and 38% will be characterized. With an increase of the indium concentration, the emission wavelengths shift from 939 to 1147 nm. For high indium concentrations, there is a strain-induced structural degradation that is manifested by an increase of the threshold current density and a decrease of the slope efficiency. (In,Ga)(As,N) edge emitting lasers comprising 35% indium and nitrogen concentrations between 1 and 3%will be characterized. The emission wavelengths shift from 1250 to 1366 nm with higher nitrogen concentrations. Concomitantly, there is an increase of the threshold current density and a decrease of the output power.