OPTICAL CHARACTERIZATION OF LOW-ENERGY NITROGEN-ION DOPED GAAS

Optical characterization of nitrogen (N)-doped GaAs was performed by l ow-temperature photoluminescence (PL) measurements, N doping in GaAs w as successfully made by irradiating low-energy (100 eV) N+ ion beam du ring the growth of GaAs using the combined ion beam and molecular beam epitaxy (CIBMBE) system, For the sample with N+ ion beam current dens ity (I-N) of 3 nA/cm(2), which correspond to N concentration ([N]) of similar to 5 x 10(17) cm(-3), two sharp PL emissions were observed at 1.508 eV (X-1) and 1.495 eV (X-2). For the sample with I-N of 75 nA/cm (2) ([N] approximate to 1 x 10(19) cm(-3)), several novel PL emissions tentatively labeled by Y-j(j=1, ..., 8) were observed in the energy r ange of 1.491-1.449 eV by furnace annealing at 750 degrees C for 20 mi n. Photoluminescence excitation measurements indicated that X-1 is cor related with the PL emission at 1.514 eV, Since the energy separation between individual Y-j(j=1, ..., 8) and X-2 is almost linear to r(k)(- 3), where r(k) is the distance between nitrogen-nitrogen (NN) pairs, w e ascribed X-2 and Y-j as the radiative transition of excitons bound t o isolated N and that to N-N pairs, respectively.