Enhanced deposition rate of sputtered amorphous silicon with a helium and argon gas mixture

Nanoscale GaN Epilayer Grown by Atomic Layer Annealing and Epitaxy at Low Temperature

“…When the R He increases above 50%, the GaN (0002) peak intensity drops dramatically, which may be deduced from too small amount of Ar ions involved in the plasma treatment. 30 Hence Figure 2b indicates that the Penning ionization leads to the increase in the amount of Ar ions in the He/Ar plasma at a low plasma power, which is beneficial to the surface heating and adatom migration at the surface. 26,31,32 Figure 2c shows the XRD ω-scan rocking curve of the reference GaN sample and the nanoscale GaN epilayer with a thickness as thin as ∼22 nm, which was prepared by ALAE with the in situ He/Ar plasma treatment (R He = 50%) at a low deposition temperature of 300 °C and a low plasma power of 50 W. The ALA treatment leads to a decrease of the FWHM of the XRD rocking curves from 379 to 168 arcsec, which is comparable to the typical FWHM of thick (>1 μm) GaN epilayers grown by MOCVD at high temperatures of 850− 1100 °C.…”

“…The result indicates that the addition of He into the Ar plasma greatly improves the crystallinity of the GaN layer, which can be explained by the so-called "Penning effect". 30 In a He/Ar mixture plasma, the presence of metastable He (denoted as He*) results in an effective increase in the ionization rate of Ar, which is described as follows:…”

“…The He has a metastable state at 19.7 eV, and the Ar has an ionization energy of 15.4 eV. 30 Hence, the energy transfer due to the collision of He* with Ar facilitates the Ar ionization. When the R He increases above 50%, the GaN (0002) peak intensity drops dramatically, which may be deduced from too small amount of Ar ions involved in the plasma treatment.…”

“…29 In addition, the Ar ionization rate can be increased by de-excitation of metastable He according to the Penning effect, despite operating at a low plasma power. 30 In this study, an in situ helium/argon (He/Ar) mixture plasma treatment at a low plasma power is used in the ALA process. High-quality nanoscale GaN epilayers are achieved via the atomic layer annealing and epitaxy (ALAE) technique on a sapphire substrate based on the layer-by-layer, in situ He/Ar plasma treatment at a low growth temperature of 300 °C.…”

“…It has been reported that the damage caused by the He plasma is less than that by the Ar plasma due to the smaller mass and momentum of He ions . In addition, the Ar ionization rate can be increased by de-excitation of metastable He according to the Penning effect, despite operating at a low plasma power …”