| The dilute-nitrides GaInNAs and GaInNAsSb show great promise in becoming the next choice for 1064 nm photodetectors and multijunction solar cells because these materials can be grown lattice-matched to GaAs and Ge substrates. One application where 1064 nm photodetectors with superior properties are required is LIGO, The Laser Interferometer Gravitational Wave Observatory. The ability to tune the bandgap of the dilute nitrides between 0.9 eV and 1.4 eV while maintaining the lattice constant of GaAs or Ge, also makes them ideal candidates for multijunction solar cells grown on GaAs or Ge substrates. In this dissertation, metamorphic InGaAs, lattice-matched GaInNAs and GaInNAsSb, PIN double heterostructures grown on GaAs substrates by molecular beam epitaxy with a RF-plasma nitrogen cell are presented. The structural, optical, and electrical properties of the films were characterized using techniques including, high-resolution x-ray diffraction reciprocal space mapping, spectral cathodoluminescence imaging, time-resolved and temperature-dependent photoluminescence, and deep-level transient spectroscopy. The internal quantum efficiency (IQE) of back-illuminated GaInNAs(Sb) photodiodes is somewhat lower than comparable metamorphic InGaAs devices due mainly to a thinner absorbing region (IQE is 60% and 75%, respectively, and absorbing layers are 1 micron and 2 microns, respectively). The device efficiencies are limited by free-carrier absorption in the substrate. If this loss were eliminated, device efficiency would increase to 90% and 75% for the InGaAs and GaInNAs(Sb) devices respectively, which indicates that both materials systems could yield photodiodes with properties comparable to commercially available InP-based detectors. All aspects of the GaInNAs solar cell performance are improved dramatically when the deflection plates are employed during growth. Additionally, the GaInNAsSb solar cells show substantially higher internal quantum efficiency (79%) than the GaInNAs devices grown using the deflection plates (67%) due to wide depletion widths, but reduced power conversion efficiency due to depressed fill-factor and open-circuit voltage. Thus, the incorporation of antimony does appear to degrade the materials quality of the thick dilute nitride films, however, the low bandgaps and excellent collection efficiency achieved from the GaInNAsSb cells is very promising. |
