Impact of the AlN nucleation layer on the variation of the vertical-direction breakdown voltage of AlGaN/GaN high-electron-mobility transistor structures on a Si substrate

Abstract

The growth conditions of the AlN nucleation layer (AlN NL) by focusing on the partial pressure of trimethyl aluminum (TMA) with a constant V/III ratio are optimized. The relationship between the size and the density of the surface pits of the AlN NL and the variation in the vertical‐direction breakdown voltage (VDBV) in the AlGaN/GaN high‐electron‐mobility transistor (HEMT) structure is determined. The maximum size of the pits in the surface of the AlN NL decreases as the partial pressure of TMA decreases. The density and the maximum size of the pits on the surface of the AlN NL decreased as the growth rate of AlN NL decreased. The pit density of the AlN NL decreases as the thickness of the AlN NL increased from 157 to 207 nm. Furthermore, the pit density is saturated when the thickness of the AlN NL was 207 nm. The optimum value of the thickness of AlN NL was about 200 nm. The variation in the VDBV of the HEMT structure decreases as the full width at half maximum (FWHM) of the rocking curve of the AlN (002) and AlN (102) planes, the pit density, and the maximum size of the pits in the AlN NL decrease. Thus, the variation in the VDBV of the HEMT structure can be related with the process of regrowth over the AlN NL.

First demonstration of X-band AlGaN/GaN high electron mobility transistors using free-standing AlN substrate over 15 W mm−1 output power density

“…27,28) However, for the HEMTs on SiC substrates, AlGaN buffers with an Al composition of more than 15% have a large difference of lattice constant from the substrate with remarkable dislocations in HEMT structures. [29][30][31] Nevertheless, AlGaN buffers with a high Al composition can be grown with low dislocations on AlN substrates. In this experiment, AlGaN buffer with an Al composition of 30% was applied for HEMT structures using AlN substrates and the back-barrier effect was evaluated.…”

Ultralow-Supersaturation Al Pretreatment toward Low Dislocation Density and Low Radio Frequency Loss GaN/AlN Epi-Stacks on High-Resistivity Si Substrates

“…For sample A, many dark pits are observed, even though it shows a relatively smooth surface. These pits are commonly observed in AlN on Si grown under conventional conditions, such as low temperatures, high growth rates, and high V/III ratios. − They can affect the stress management as well as the buffer leakage. , Here, the formation of the pits was attributed to the considerably low growth temperature (980 °C), which is far from the optimum AlN growth conditions (∼1100 °C). However, these pits could be eliminated by lowering the TMAl flow rate in the pretreatment process (sample E).…”

Impact of In Situ Annealing on the Deep Levels in Ni‐Au/AlN/Si Metal–Insulator–Semiconductor Capacitors

“…This reduces the vertical breakdown voltage of GaN‐based power devices . Also the presence of surface pits in the AlN nucleation layer can affect the vertical breakdown behavior . In addition, the increased conductivity of the silicon substrate by the Al (or Ga) in‐diffusion and the associated GR center formation creates a parasitic conduction path, which enhances losses in the radio frequency (RF) range .…”

“…[14][15][16][17][18][19] Also the presence of surface pits in the AlN nucleation layer can affect the vertical breakdown behavior. [20] In addition, the increased conductivity of the silicon substrate by the Al (or Ga) in-diffusion and the associated GR center formation creates a parasitic conduction path, which enhances losses in the radio frequency (RF) range. [21,22] It is, therefore, important to characterize the AlN/silicon interface and the defects present at both sides of the interface and at the interface.…”