Novel dilute III–V-Ns : From physics to applications

Unlike the conventional III-V semiconducting alloys where a smaller lattice constant generally causes an increase in the band gap, a smaller covalent radius of N with a larger electronegativity causes a strong bowing parameter in dilute III-V-Ns. Consequently the addition of N in GaAs or InGaAs decreases the band gap (E_g) dramatically. This strong dependence of E_g on the N content in III-As-N has provided opportunities to engineer many material properties suitable for the fiber-optical communications at 1.3 and 1.55 ?m wavelengths as well as in designing high efficiency solar cells. The purpose of this talk is to address important issues required for understanding the physics and technology of novel dilute III-V-Ns- especially to comprehend the role of N in such materials. We will present the results of our comprehensive analyses of the Fourier transform infrared (FTIR) absorption and Raman scattering data on impurity modes in dilute ternary GaAs_1-xN_x, [GaAs_1-xN_x] (x < 0.03) and quaternary InGaAs(P)N alloys grown on GaAs [GaP] by metal organic chemical vapor deposition (MOCVD) and solid source molecular beam epitaxy (MBE). For the low composition of N in GaAs_1-xN_x [GaAs_1-xN_x] (i.e., x < 0.015), we find that most of the N atoms occupy the As [P] sublattice NAs [N_P]. They prefer, however, moving out of their substitutional sites to more energetically favorable locations at higher x values. To comprehend the large width of the localized vibrational mode (LVM) observed in GaAs_1-xN_x near 470 cm^-1, we have studied the possibilities of Ga-isotopes (⁶⁹Ga and ⁷¹Ga) and/or intrinsic defects participating with NAs in different configurations. Results for the N-local modes and its isotopic shifts are found in good agreement with the FTIR data. Although, the presence of isolated N- interstitial (N- sub>int) in GaAs_1-xN_x is quite unlikely at higher compositions (0.03 > x > 0.015), the formations of non-radiative complex microstructures involving N and/or intrinsic defects are energetically favorable. We discuss the role of such defects on the performance of electronic devices especially photo-detectors and long wavelength vertical cavity surface-emitting lasers (VCSELs).