Comparison of Hydrogen-Induced Oxide Charges Among GaN Metal-Oxide-Semiconductor Capacitors with Al₂O₃, HfO₂, or Hf_0.57Si_0.43O_x Gate Dielectrics

Abstract

The effect of hydrogen on GaN metal-oxide-semiconductor (MOS) capacitors with Al2O3, HfO2, or Hf0.57Si0.43O x gate dielectrics was studied using capacitance–voltage (C–V) measurements. Hydrogen exposure shifted all the C–V curves toward the negative bias direction, and the hydrogen response of the devices was reversible. When the hydrogen-containing ambient atmosphere was changed to N2, the C–V characteristics were found to gradually revert to the initial values in N2. Application of a reverse gate bias accelerated the reversion compared with that in the absence of a bias, indicating that hydrogen was absorbed into the dielectric (Hf0.57Si0.43O x ) as positive mobile charges. This result is consistent with the direction of the shift of the C–V curves; positively charged hydrogen absorbed into a dielectric can cause a flatband voltage shift. The hydrogen-induced shift of the C–V curves varied depending on the dielectric. MOS devices with HfO2-based high-k dielectrics were found to have approximately two to four times more incorporated charges than devices with Al2O3. Under the hypothesis that oxygen vacancies (VOs) trap hydrogen, the obtained results imply that the number of VOs in HfO2-based high-k dielectrics is much larger than that in Al2O3-based dielectrics.

High photoresponsivity MoS2 phototransistor through enhanced hole trapping HfO2 gate dielectric

“…where V 0 was the gate voltage axis intercept obtained from the linear extrapolation of the transfer curve at the point of the maximum transconductance. The V th of the sample with H 2 annealing exhibited a negative shift relative to that of the sample without annealing, indicating H 2 annealing introduces positive charge traps at the HfO 2 interface [19]. The sub threshold swing was measured to be 200 and 187 mV dec −1 for the phototransistor without annealing and with H 2 annealing, respectively.…”

Pt/GaN Schottky Barrier Height Lowering by Incorporated Hydrogen

“…3 and Table I), the N D − N A value for the Pt/GaN SBD in 1% H 2 + N 2 mixture gas is the same as that for the device in pure N 2 gas; therefore, hydrogen exposure does not change the electrical properties of the GaN layers. According to our previous study involving GaN MOS capacitors, 13 oxide layers between Pt and GaN are the most likely origin of the change in the Pt/GaN interface oxide resistance because hydrogen was found to be absorbed into the oxide layers as positive mobile charges. Third, hydrogen-induced property changes in oxides have been reported for various oxides, including TiO 2 , 21 Ta 2 O 5 , 22 HfO 2 , 23 Pb(Zr,Ti)O 3 , 24 SrBi 2 Ta 2 O 9 , 25 SrTiO 3 , 26 and BaTiO 3 ; 27 hydrogen is known to reduce the resistance of these oxides.…”

“…12 With respect to GaN metal-oxidesemiconductor (MOS) capacitors, by contrast, we recently reported that ambient hydrogen was incorporated into dielectric layers as positively charged mobile ions, leading to flatband voltage shifts of the devices. 13 In that report, we revealed that oxide layers in MOS devices played a critical role in the flatband voltage shifts; that is, we speculated that the flatband voltage shifts originated from trapped hydrogen at oxygen vacancies (V O s) in the oxide layers. 13 In addition, even for GaN SBDs, we found that the formation of oxides at the Pt/GaN interface might be responsible for the reduction of the Schottky barrier height (Φ B ) as a result of hydrogen exposure.…”

“…13 In that report, we revealed that oxide layers in MOS devices played a critical role in the flatband voltage shifts; that is, we speculated that the flatband voltage shifts originated from trapped hydrogen at oxygen vacancies (V O s) in the oxide layers. 13 In addition, even for GaN SBDs, we found that the formation of oxides at the Pt/GaN interface might be responsible for the reduction of the Schottky barrier height (Φ B ) as a result of hydrogen exposure. 14,15 That is, we hypothesized that hydrogen trapped at V O s in the Pt/GaN interface oxide changed the resistivity of the oxide layers, resulting in the Φ B reductions.…”

“…In our previous study involving GaN MOS capacitors, the application of a reverse gate bias during the reversion revealed the charging state of hydrogen in the oxide layers. 13 For GaN SBDs, however, the charging state of hydrogen is unknown. In the present study, we used current-voltage (I-V), capacitance-voltage (C-V), impedance spectroscopy, and current-time (I-t) measurements to investigate the charging state, along with the hydrogen response and reversion characteristics, of Pt/GaN SBDs.…”