Effect of substrate-induced strain in the transport properties of AlGaN/GaN heterostructures

Abstract

This paper studies the effect of substrate-induced strain in the transport properties of AlGaN/GaN heterostructures grown on Si substrates by metal-organic chemical vapor deposition. Partial thinning of the original Si substrate by chemical dry etching has been used to induce controllable amounts of biaxial strain in the sample. After each etching step, Raman and Hall effect—Van Der Pauw measurements were performed as a function of remaining Si substrate thickness to study the residual biaxial strain and transport properties of the two-dimensional electron gas (2DEG). A 25% increase in the 2DEG density was obtained after removal of ∼30% of the total Si thickness. In addition, a 20% higher electron mobility has been observed under biaxial strain increase. This new technology has been applied to standard AlGaN/GaN transistors grown on Si substrates to increase their maximum current density by ∼20%.

Low-Loss and High-Voltage III-Nitride Transistors for Power Switching Applications

“…Azize and Palacios [66] reported a mobility increase by etching a Si substrate from the backside for controlling the tensile strain in AlGaN. Fehlberg et al [67] reported a high mobility of 2380 cm 2 /V s by depositing SiN films with varied deposition conditions, resulting in introduction of strain in an AlGaN layer.…”

Influence of sapphire substrate thickness on the characteristics of AlGaN/AlN/GaN heterostructure field-effect transistors

“…The stress variation is quite different from that with a Si substrate as described in Ref. [14]. Before Si substrate thinning, the original stress (strain) of the GaN layer is tensile stress, which is mainly due to the thermal expansion mismatch between the GaN layer and Si substrate [17].…”

“…When the temperature is reduced from the growth temperature to the room temperature, in-plane tensile stress (for Si substrate) and compressive stress (for sapphire substrate) in GaN layer are induced, respectively. And, when the remaining Si substrate thickness decreases, the tensile stress firstly increases (more than 350 µm Si thickness remaining) and then induces a relaxation (less than 350 µm Si thickness remaining) [14]. When the sapphire substrate thickness decreases, the compressive stress tends to increase for the remaining sapphire substrate thickness less than 170 µm.…”

“…However, due to the lattice and thermal misfits between the substrate and the epilayers, there is residual strain in the GaN layer for the AlGaN/AlN/GaN heterostructures, which is one of the factors that affect the reliability of AlGaN/AlN/GaN HFETs [12,13]. For AlGaN/GaN heterostructures with Si substrate, the effects induced by substrate thickness have been studied, and the in-plane strain of GaN layer changes with the substrate thickness variation [14]. The sapphire substrate is also one of the most important substrates for GaN epitaxy [1,8,12,13], and is with different lattice and thermal expansion coefficients comparing with a Si substrate.…”

Influence of strain induced by AlN nucleation layer on the electrical properties of AlGaN/GaN heterostructures on Si(111) substrate

“…The externally induced tensile stress enhances piezoelectric polarization charge density which results in high sheet carrier density and increased mobility through techniques like substrate thinning and vacuum annealing. 15,16 But in our case, unlike the externally induced residual stress, the internal residual strain only degrades rather improve the electrical properties of the heterostructures.…”