Ultrahigh Si+ implant activation efficiency in GaN using a high-temperature rapid thermal process system

Abstract

Si + implant activation efficiencies above 90%, even at doses of 5×1015 cm−2, have been achieved in GaN by rapid thermal processing at 1400–1500 °C for 10 s. The annealing system utilizes molybdenum intermetallic heating elements capable of operation up to 1900 °C, producing high heating and cooling rates (up to 100 °C s−1). Unencapsulated GaN shows severe surface pitting at 1300 °C and complete loss of the film by evaporation at 1400 °C. Dissociation of nitrogen from the surface is found to occur with an approximate activation energy of 3.8 eV for GaN (compared to 4.4 eV for AlN and 3.4 eV for InN). Encapsulation with either rf magnetron reactively sputtered or metal organic molecular beam epitaxy-grown AlN thin films provides protection against GaN surface degradation up to 1400 °C, where peak electron concentrations of ∼5×1020 cm−3 can be achieved in Si-implanted GaN. Secondary ion mass spectrometry profiling showed little measurable redistribution of Si, suggesting DSi⩽10−13 cm2 s−1 at 1400 °C. The implant activation efficiency decreases at higher temperatures, which may result from SiGa to SiN site switching and resultant self-compensation.

Rapid Thermal Processing of Implanted GaN up to 1500°C

“…We have found that Si, the most common n-type dopant, shows no detectable redistribution at 1400 °C, and that annealing at this temperature produces activation percentages of ≥90% [19,20]. Annealing at 1500 °C led to a reduction in both sheet electron concentration and electron mobility, which is consistent with self-compensation through site-switching of the Si.…”

“…13 cm -2 , corresponds to a peak volume density of ~5×10 18 cm -3 . This is well below that achieved with Si + implantation and annealing (>10 20 cm -3 ) [17,20]. In the latter case the carrier density showed an activation energy of 5.2 eV.…”

Searching for better plasmonic materials

“…However, to bring the crossover frequency near the optical range, a doping level of at least 3 ¢ 10 20 cm 3 is required. The necessity of doping semiconductors so heavily raises concerns about the solid solubility limit, the fraction of dopants that would be active, and doping compensation effects [116,117]. Another major concern at such high doping levels is retaining the high carrier mobility that is essential for low losses.…”

Failure mechanism of AlN nanocaps used to protect rare earth-implanted GaN during high temperature annealing

“…However, some localized failures of the AlN caps are observed; several groups have reported pitted surfaces in Siimplanted AlN capped GaN after annealing at temperatures higher than or equal to 1300°C. 3,[7][8][9] The structure of these pits and the mechanism that leads to their formation has not been fully explained. In this letter, we present the microscopic study of the failure mechanisms of such caps in relation to the protection that they provide during high temperature annealing of RE implanted GaN epilayers providing clear indications for producing caps with a higher resistance to degradation.…”

“…7-9͒, had thicknesses of 50 or 120 nm, much larger than those used in our study. Cao et al 9 discussed the possible influence of residual H 2 bubbles in the AlN layer as a source of occasional localized cap fractures. Zolper et al 4 suggested that the AlN cap on Si-implanted GaN might fail due to poorly defined stoichiometry, or the evolution of hydrogen from the GaN that could break the AlN during escape.…”