Conduction mechanism of non-gold Ta/Si/Ti/Al/Ni/Ta ohmic contacts in AlGaN/GaN high-electron-mobility transistors

Abstract

This work investigates the conduction mechanism of non-gold Ta/Si/Ti/Al/Ni/Ta ohmic contact in un-doped AlGaN/GaN high-electron-mobility transistors (HEMTs) grown on Si. The temperature dependent I-V measurement reveals that the conduction mechanism is primarily via Thermionic Emission(TE). The extracted mean barrier height(Φ B ) values are 0.113 and 0.121 eV and the mean contact resistance(R c ) values are 0.24 and 0.28 Ω•mm respectively for annealing temperature at 850 ºC and 900 ºC. The low R c is attributed to the formation of low work function Ti x Si y at the metal-semiconductor interface. The HR-TEM and EDX analysis also provide structural evidence to support the TE mechanism.

AlGaN/GaN high electron mobility transistors on Si with sputtered TiN gate

“…The extracted effective SBH is 1.105 eV, which is very close to the the SBH extracted from room temperature I – V measurement, suggesting that R s does not play a significant role in the forward conduction of TiN SBDs. However, the fitted Richardson constant value ( A* ∼ 6.36 A cm −2 K −2 ) was much smaller compared to the theoretical value of Al 0.26 Ga 0.74 N (26.4 A cm −2 K −2 ) . The large discrepancy, which was also observed by other groups , can be explained by the reduction of effective anode area , other transport mechanisms , and the influence of process parameters .…”

“…The AlGaN/GaN heterostructure was grown on a 4‐inch high‐resistivity Si (111) substrate by metal organic chemical vapor deposition (MOCVD). At room temperature, the measured two‐dimensional electron gas (2DEG) sheet carrier density was 9.8 × 10 12 cm −2 with an electron mobility of 1450 cm 2 V −1 s −1 . The device fabrication, including HEMTs and guard‐ring type Schottky barrier diodes (SBDs), started from the mesa isolation by BCl 3 /Cl 2 plasma etching.…”

Au-free recessed Ohmic contacts to AlGaN/GaN high electron mobility transistor: Study of etch chemistry and metal scheme

“…39 The conduction mechanism for Au-free contacts to AlGaN/GaN HEMTs have been discussed for nonrecessed contact schemes annealed at high temperatures of 850-900 °C (Ref. 40) and for recessed contact schemes annealed at a moderate temperature of 600 °C. 17 In these reports, temperature dependent measurements of the contact characteristics and a plot of specific contact resistivity as a function of temperature have been used to determine this mechanism.…”

“…17 In these reports, temperature dependent measurements of the contact characteristics and a plot of specific contact resistivity as a function of temperature have been used to determine this mechanism. For the nonrecessed Au-free metallization scheme, 40 thermionic emission is reported as the conduction mechanism at the Ohmic contact. This mechanism is characterized by the strong temperature dependence of specific contact resistivity on temperature.…”

Study of Au-Based and Au-Free Ohmic Contacts in AlGaN/GaN HEMTs by Recessed Patterns

“…6,7 So far, various Aufree metallization solutions have been proposed to prevent Au from becoming a heavy-metal contaminant in the fabrication of silicon devices. [8][9][10][11][12] In addition, high annealing temperature causes nitrogen deficiency and bare (Al)GaN surface oxidation problems in the device, which leads to a decrease in the dynamic performance of the device. 13,14 To avoid high annealing temperature to form ohmic contacts, other methods to obtain good ohmic contacts include forming n-type GaN at the source and drain region through regrowth or ion implantation, but the high cost and complex process hinder the development of these methods.…”