Co-doped Epilayers Research Articles

Carrier Lifetimes and Influence of In-Grown Defects in N-B Co-Doped 6H-SiC

The thick N-B co-doped epilayers were grown by the fast sublimation growth method and the depth-resolved carrier lifetimes have been investigated by means of the free-carrier absorption (FCA) decay under perpendicular probe-pump measurement geometry. In some samples, we optically reveal in-grown carbon inclusions and polycrystalline defects of substantial concentration and show that these defects slow down excess carrier lifetime and prevent donor-acceptor pair photo luminescence (DAP PL). A pronounced electron lifetime reduction when injection level approaches the doping level was observed. It is caused by diffusion driven non-radiative recombination. However, the influence of surface recombination is small and insignificant at 300 K.

Room-temperature ferromagnetism in Mn-N Co-doped p-ZnO epilayers by metal-organic chemical vapor deposition

Mn-N co-doped Zn epilayers were grown by metal-organic chemical vapor deposition. The Mn-N co-doped epilayers exhibit single phase hexagonal wurtzite structure, indicative of the small lattice damage from co-doping. Secondary ion mass spectroscopy analysis indicates that Mn and N atoms have been in situ incorporated into the ZnO epilayer. Hall measurements exhibit the conduction transition from n-type of the N mono-doped ZnO to p-type of the Mn-N codoped ZnO epilayer. This behavior is attributed to the low formation energy of Mn-N neighboring bonds in the co-doped epilayers. Mn doping leads to the low incorporation of N-H and N-N complexes, which are abundant in the N mono-doped epilayer and always act as compensation centers of holes. Moreover, room temperature ferromagnetism has been observed on the above co-doped epilayer, which is possibly due to the hole mediation on the ferromagnetic ordering of Mn atoms.

Correlation between carrier recombination and p-type doping in P monodoped and In–P codoped ZnO epilayers

The carrier recombination processes in p-type ZnO epilayers with P monodoping and In–P codoping have been studied by temperature-dependent photoluminescence spectroscopy. Good correlations were observed between carrier recombination and acceptor and donor energy levels. The exciton transition feature of acceptor-bound excitons (3.350eV), the free electron-acceptor emission (3.315eV), and the donor-acceptor-pair emission (3.246eV) exhibited different carrier recombination associated various defect complexes. The origins of two broad emissions at ∼2.99 and ∼2.89eV were found to be due to different photoelectron radiative transitions associated with deep level acceptors (isolated Zn vacancies). The acceptor-bound energies for P monodoped and In–P codoped epilayers ∼195 and ∼127meV, respectively. The small binding energy is helpful for acceptor ionization at room temperature, resulting in a high hole concentration in the codoped epilayer.

Optical properties of Mn4+ ions in GaN:Mn codoped with Mg acceptors

The optical properties of Mn–Mg-codoped epitaxial GaN were studied. Addition of Mg acceptors quenches the weak manganese-related photoluminescence (PL) band at 1.3eV in GaN:Mn and a series of sharp PL peaks are observed at 1eV in codoped epilayers. The change in PL spectra indicates that the Mg addition stabilizes the Mn4+ charge state by decreasing the Fermi level. The 1eV PL peaks are tentatively attributed to intracenter transitions involving Mn4+ ions. Spin-allowed 3d-shell T24–T14 transitions and their phonon replicas are involved. The relative intensities of the sharp peaks are strongly dependent on the excitation wavelength, indicating that the optically active Mn4+ centers involved in the separate peaks are different. The temperature dependence of the PL spectrum suggests the presence of at least three distinct Mn4+ complex centers.