P-type conductivity and suppression of green luminescence in Mg/N co-implanted GaN by gyrotron microwave annealing

Abstract

Co-implantation of Mg with N has been shown to improve p-type conductivity in Mg-implanted GaN. Achievement of p-type material still requires temperatures beyond the thermodynamic stability of GaN, however. In this study, we present results of implantation and anneal activation of GaN, co-implanted with Mg and N or Mg only by repeated, short thermal cycles of 1350 °C using a high-power gyrotron microwave source with a quasi-gaussian intensity profile. Spatial variations in optical and electrical properties of the resulting films are characterized by photoluminescence and diode I–V and C–V measurements. Resistive Mg/N co-implanted and annealed material shows dominant luminescence of the VN-related green luminescence (GL2) band at 2.37 eV and relatively lower intensity acceptor-related ultraviolet luminescence (UVL) at 3.27 eV. However, a material showing p–n diode behavior shows higher-intensity UVL luminescence and suppression of the GL2 band, permitting observation of the yellow luminescence (YL) present in the as-grown GaN. The YL is attributed to unintentionally introduced CN–ON complexes and is commonly observed in GaN grown by metalorganic chemical vapor deposition but is typically absent in implanted/annealed GaN. Co-implanted material is compared to material implanted only with Mg and annealed under the same conditions, which shows p-type activation, but contains persistent GL2 luminescence post-anneal and lowers maximum hole concentration.

Novel Codoping Moiety to Achieve Enhanced P‐Type Doping in GaN by Ion Implantation

“…With the addition of nitrogen to improve the stoichiometric balance, shown in Figure 3e, the defect band at %530 nm shows a decreased intensity after the 1530 °C SMRTA20, consistent with published observations and attributed to a reduction in the resultant vacancy population. [46,53] In the case of codoping with oxygen donors (ADA-O) seen in Figure 3d,f, a similar trend is observed; however, the UVL enhancement upon incorporation of the oxygen is over an order of magnitude greater than with silicon. Furthermore, the defect luminescence bands appear to have a concomitant greater reduction upon nitrogen compensation implantation.…”

“…The enhanced hole concentrations evident with oxygen incorporation reveal important considerations for device design given unintentional doping during growth and future incorporation of ion implantation capabilities. multicycle rapid thermal annealing (SMRTA), [22][23][24][25][26][27][28][29][30][31][32][33][34] ultrahighpressure annealing (UHPA), [35][36][37][38][39][40][41][42][43] gyrotron annealing, [44][45][46] microwave annealing, [47] and standard rapid thermal annealing. [48][49][50] Here we have utilized ion implantation to explore p-type dopant activation enhancement using the novel codoping moiety of introducing both acceptors and donors at a 2:1 ratio for formation of ADA complexes.…”

“…While ion implantation allows precise control of dopant location, depth, concentration, and total dose, at the time, the need for annealing and subsequent difficulties did not warrant investigation. In the intervening years, ion‐implanted magnesium activation has been attempted or demonstrated in GaN as well as forming devices such as p–i–n diodes, junction barrier Schottky (JBS) diodes, and metal‐oxide‐semiconductor field effect transistors (MOSFET) via multiple annealing techniques such as symmetric multicycle rapid thermal annealing (SMRTA), [ 22–34 ] ultrahigh‐pressure annealing (UHPA), [ 35–43 ] gyrotron annealing, [ 44–46 ] microwave annealing, [ 47 ] and standard rapid thermal annealing. [ 48–50 ] Here we have utilized ion implantation to explore p‐type dopant activation enhancement using the novel codoping moiety of introducing both acceptors and donors at a 2:1 ratio for formation of ADA complexes.…”

Photoluminescence from Vacancy‐Containing Defects in GaN

“…[30] The GL2 band is observed only in high-resistivity (semi-insulating) GaN, usually undoped GaN grown in extremely Ga-rich conditions and GaN doped or implanted with acceptors such as Mg or Be. [21,30,[34][35][36][37][38] It can be distinguished from other PL bands in this spectral region by specific features. In particular, its decay after a pulse excitation is exponential at T < 20 K, with the characteristic PL lifetime (τ) of 250 μs, and the band is relatively narrow.…”

Ion Implantation into Nonconventional GaN Structures

“…Anderson et al [81] used an AlN cap combined with multi-cycle annealing with a peak temperature around 1350 • C to achieve activation close to the theoretical limit. Similar multi-cycling annealing was used by Meyers et al who furthermore showed that Mg/N co-implantation yields improved p-type conductivity, presumably due to the suppression of nitrogen vacancy formation [84]. The conversion of a low-dislocation density n-type GaN layer to p-type using Mg-implantation and the formation of a p-n junction was achieved after annealing at 1230 • C using a SiN cap [85].…”