Fabrication and Performance of Ti/Al/Ni/TiN Au-Free Ohmic Contacts for Undoped AlGaN/GaN HEMT

Au‐Free Ohmic Contacts and Their Impact on Sub‐Contact Charge Carrier Concentration in AlGaN/GaN Heterostructures

“…The lowest contact resistance was achieved for the last sample annealed at T RTA ¼ 900 C with R c ¼ 0.74 Ω mm. This is in the expected range for non-recessed Ti/Al-based Au-free contact metallization schemes, which have resistances between 1.1 and 0.4 Ω mm after annealing at 500⋯900 C. [4,[21][22][23][24][25] If using a pre-deposition recess etching step of the sub-contact area, contact resistances between 0.6 and 0.2 Ω mm can be achieved after annealing at 600⋯550 C. [26][27][28][29] The RMS surface roughness for this sample was as low as 4.6 nm (measured over a length of 1500 μm, using high-resolution profilometry). The similar shape of Figure 5 and 7 in the region between T RTA ¼ 650⋯850 C seems to indicate that the total resistance R total of the test device is dominated by the contact resistance R c .…”

Effect of TiN barrier layer in Cu-based ohmic contact of AlGaN/GaN high electron mobility transistor

“…Wide bandgap GaN and its related materials have been widely investigated in recent years for high-frequency and * Author to whom any correspondence should be addressed. high-power electronics applications [1][2][3][4], largely because of their enabling physical properties that demonstrate high-level performances in electron mobility, threshold breakdown field, saturation velocity, operating temperature, and carrier density of two-dimensional electron gas [5]. For wireless communications [6], radar sensing [7], and satellite broadcasting [8] applications, high-electron-mobility transistors (HEMTs) based on AlGaN/GaN have been under intense research mostly because of their superior highfrequency device characteristics.…”

Reduction in RF Loss Based on AlGaN Back-Barrier Structure Changes

“…The GaN HEMT device usually introduces an AlN nucleation layer between the Si substrate and the GaN layer, but its Al atoms will diffuse on the surface and on the inside of the Si substrates to form a conductive layer, which will cause RF loss in the devices working at high frequency and results in limiting output power and efficiency [11]. According to reports, wafer warpage caused by mismatch is greatly improved by adding a suitable Al(Ga)N stress control layer [12], and gold-free ohmic contacts technology has achieved a breakthrough in the compatibility issue mentioned above [13]. However, the problem of RF loss has become an urgent problem to be solved at present.…”