Influence of Al content on electrical and structural properties of Si‐doped Al _x Ga _1–x N/GaN HEMT structures

Abstract

Improved electrical properties of Al x Ga 1-x N/GaN high electron mobility transistor (HEMT) structures grown by metalorganic chemical vapor deposition (MOCVD) were achieved through increasing the Al mole fraction in the AlGaN barrier layers. An average sheet resistance of 326.6 Ω/sq and a good resistance uniformity of 98% were obtained for a 2-inch Al 0.38 Ga 0.62 N/GaN HEMT structure. The surface morphology of Al x Ga 1-x N/GaN HEMT structures strongly correlates with the Al content. More defects were formed with increasing Al content due to the increase of tensile strain, which limits further reduction of the sheet resistance.

Growth Temperature Dependency of High Al Content AlGaN Epilayers on AlN/Al2O3 Templates

“…We have both kinds of spiral growth types for the lower growth temperature (sample A). With the decreasing of Al content in AlGaN epilayer, the strain increases, leading to more defects [17]. For the increasing growth temperatures (increased Al content in AlGaN) it seems that AlGaN surfaces don't have spiral growth mode anymore which indicates the decreasing number of density of dislocations.…”

Analyses of 2-DEG characteristics in GaN HEMT with AlN/GaN super-lattice as barrier layer grown by MOCVD

“…However, the relatively low carrier sheet density with AlGaN/GaN structures hinders the further development of device process. Although the sheet carrier density can be further improved by increasing the Al content in the ternary barrier layer, this increases the strength of polarization; on the other hand, increasing the Al content in the ternary layer may deteriorate the quality of AlGaN due to large lattice mis-match, and ternary alloy scattering in the hetero-structure resulted in poor transport properties [7]. In contrast, the growth of AlN barrier layer on GaN channel enhances the transport properties.…”

Structural, morphological, and optical properties of AlGaN/GaN heterostructures with AlN buffer and interlayer

“…For instance, an AlGaN ternary layer ͑TL͒ was doped with silicon in order to increase 2DEG density but this increase was rather limited. 5,6,12 In other studies, an increase of Al content in the AlGaN TL resulted in an increase in 2DEG density due to stronger spontaneous polarization and piezoelectric effects, [13][14][15] but electron mobility was reduced due to the enhancement of lattice stress, interface roughness, and alloy disorder scattering. [16][17][18][19] Apart from these methods, it has been found that the insertion of an AlN interlayer ͑IL͒ between an AlGaN TL and a GaN buffer layer ͑BL͒ ͑AlGaN/ AlN/GaN͒ remarkably improves 2DEG density and electron mobility, due to the larger conduction band offset ͑⌬E c ͒ induced by the AlN IL and the decreased alloy disorder.…”