Origin of positive fixed charge at insulator/AlGaN interfaces and its control by AlGaN composition

Abstract

The key feature for the precise tuning of Vth in GaN-based metal-insulator-semiconductor (MIS) high electron mobility transistors is the control of the positive fixed charge (Qf) at the insulator/III-N interfaces, whose amount is often comparable to the negative surface polarization charge (Qpol−). In order to clarify the origin of Qf, we carried out a comprehensive capacitance-voltage (C-V) characterization of SiO2/AlxGa1–xN/GaN and SiN/AlxGa1–xN/GaN structures with Al composition (x) varying from 0.15 to 0.4. For both types of structures, we observed a significant Vth shift in C-V curves towards the positive gate voltage with increasing x. On the contrary, the Schottky gate structures exhibited Vth shift towards the more negative biases. From the numerical simulations of C-V curves using the Poisson's equation supported by the analytical calculations of Vth, we showed that the Vth shift in the examined MIS structures is due to a significant decrease in the positive Qf with rising x. Finally, we examined this result with respect to various hypotheses developed in the literature to explain the origin of the positive Qf at insulator/III-N interfaces.

Comparative Study of Characteristics and Interface States with and without Post‐Gate‐Annealing Treatment for AlGaN/GaN‐Recessed Metal–Insulator–Semiconductor High Electron Mobility Transistors Using HfO2 Gate Insulator on Si Substrates

“…The interface states are in the form of trap states and fixed charges . Fixed charges that are positively charged at the HfO 2 /AlGaN interface make the V th shift negatively, and the decrease of fixed charges makes the V th shift positively . The trap states without electrons are neutral .…”

“…[14] Fixed charges that are positively charged at the HfO 2 /AlGaN interface make the V th shift negatively, and the decrease of fixed charges makes the V th shift positively. [17] The trap states without electrons are neutral. [14] As the barrier layer becomes thinner, the trap states that are more likely to capture electrons from the channel make the V th shift positively, and the decrease of trap states makes the V th shift negatively.…”

Vacancy-type defects in Al2O3/GaN structure probed by monoenergetic positron beams

“…positive charges fixed at the interface. 16,19,20 The V fb value increased as the annealing temperature increased, suggesting that the density of net positive charges decreased due to annealing up to 900 C. Under illumination, the value of V fb decreased, but the difference between the values measured with and without illumination decreased as the annealing temperature increased. We will come back to this point later.…”

“…[6][7][8][9] Thus, techniques for depositing oxide or nitride films on GaN and their electrical properties have been extensively studied. [10][11][12][13][14][15][16][17][18][19][20] Among many candidates, Al 2 O 3 prepared using atomic layer deposition (ALD) is seen as an attractive candidate for GaN-based MOS devices because of its high conduction-band offset on GaN, high dielectric constant, and high breakdown field.…”

ALD Al2O3, SiNx, and SiON films as passivating coatings in AlGaN/GaN HEMT

“…Для этих целей в качестве эффективных покрытий обычно используются низкотемпературные пленки, выращенные с помощью плазмохимического осаждения из газовой фазы (PECVD), атомно−слое вого осаждения (ALD) и плазменно−стимулированного осаж дения (PE A L D). Д л я г етеростру кт у р AlGaN/GaN наиболее перспективными и чаще всего используемые являются следующие пленки: ALD Al 2 О 3 (Е G = 6÷8 эВ, ε = 8÷10), SiN х (Si 3 N 4 , Е G = 5÷6 эВ, ε = 7÷7,2), SiON, ALD AlN (Е G = 6 эВ, ε = 8÷9) [1][2][3][4]. Несмотря на наличие ряда работ по анализу поверхностных состояний на границе диэлектрик/AlGaN и имеющиеся теоретические расчеты [3][4][5] в каждом конкретном случае остается ряд нерешенных проблем, связанных с границей раздела изолятор/ AlGaN.…”