Origin(s) of Anomalous Substrate Conduction in MOVPE-Grown GaN HEMTs on Highly Resistive Silicon

Abstract

The performance of transistors designed specifically for high-frequency applications is critically reliant upon the semiinsulating electrical properties of the substrate. The suspected formation of a conductive path for radio frequency (RF) signals in the highly resistive (HR) silicon substrate itself has been long held responsible for the suboptimal efficiency of as-grown GaN high electron mobility transistors (HEMTs) at higher operating frequencies. Here, we reveal that not one but two discrete channels distinguishable by their carrier type, spatial extent, and origin within the metal-organic vapor phase epitaxy (MOVPE) growth process participate in such parasitic substrate conduction. An ntype layer that forms first is uniformly distributed in the substrate, and it has a purely thermal origin. Alongside this, a p-type layer is localized on the substrate side of the AlN/Si interface and is induced by diffusion of group-III element of the metal-organic precursor. Fortunately, maintaining the sheet resistance of this p-type layer to high values (∼2000 Ω/□) seems feasible with particular durations of either organometallic precursor or ammonia gas predose of the Si surface, i.e., the intentional introduction of one chemical precursor just before nucleation. It is proposed that the mechanism behind the control actually relies on the formation of disordered AlSiN between the crystalline AlN nucleation layer and the crystalline silicon substrate.

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

“…The region of the spatial shift between Al and N was assigned to an intermixed Al-Si-N layer at the AlN/Si interface. 15,34 For sample E, a similar shift was also observed, but with a smaller amplitude of only 0.2 nm, as shown in Figure 3b. It indicates that the formation of the amorphous Al-Si-N interlayer has been effectively suppressed and a sharper AlN/Si heterointerface has been achieved via the USAP approach.…”

“…25−28 In order to further confirm these results, transmission electron microscopy (TEM) experiments were performed. Panels (a and b) and (c and d) in Figure 1 show the bright-field TEM images under two-beam conditions with g = [0002] and g = [11][12][13][14][15][16][17][18][19][20] for sample A (with conventional pretreatment conditions) and sample E, respectively. It is again shown that both screw-and edge-type threading dislocations in sample E are significantly reduced compared to those in sample A.…”

“…The possible origins of the parasitic conductive channel could be the electron inversion layer and the p -type channel due to Al and/or Ga atom diffusion into Si substrates. The latter is suggested to play a crucial role, − especially at high growth temperatures. In order to suppress the diffusion, various approaches have been attempted, such as reducing the growth temperature − and introducing a 3C-SiC layer or SiN x blocking layer .…”

Additive GaN Solid Immersion Lenses for Enhanced Photon Extraction Efficiency from Diamond Color Centers

“…A schematic of the process flow is indicated in Figure while corresponding experimental results are shown in Figure . Figure a illustrates how the GaN solid immersion lenses are defined and suspended on a strain-optimized heteroepitaxially grown GaN-on-Si chip − based on the wafer-scale compatible microfabrication process reported in earlier study . Initially, polymer resist lenses are defined by grayscale lithography and thermal reflow (1), followed by inductively coupled plasma (ICP) dry etching to transfer the lens shape into the 2 μm thick GaN top layer (2).…”

Reduction in RF Loss Based on AlGaN Back-Barrier Structure Changes

“…Structure Loss Time Meneghesso G. [29] Si/(AlGa)N/GaN/AlN 0.9 dB/mm @ 10 GHz 2013 Cao L. [30] Si/(AlGa)N/GaN/AlGaN 0.58 dB/mm @ 5 GHz 2017 Cordier Y. [15] Si/(AlGa)N/GaN 0.3 dB/mm @ 10 GHz 2018 Cao L. [20] Si(HR)/(AlGa)N/GaN/AlGaN 0.27 dB/mm @ 20 GHz 2018 Chandrasekar H. [28] GaN-on-Si 0.6 dB/mm @ 6 GHz 2019 Wei L. [11] Si/AlN 1.47 dB/mm @ 6 GHz 2020 Ghosh S. [31] Si/AlN 12.7 dB/mm @ 5 GHz 2021 Si/(AlGa)N/GaN/AlN 0.9 dB/mm @ 10 GHz 2013 Cao L. [30] Si/(AlGa)N/GaN/AlGaN 0.58 dB/mm @ 5 GHz 2017 Cordier Y. [15] Si/(AlGa)N/GaN 0.3 dB/mm @ 10 GHz 2018 Cao L. [20] Si(HR)/(AlGa)N/GaN/AlGaN 0.27 dB/mm @ 20 GHz 2018 Chandrasekar H. [28] GaN-on-Si 0.6 dB/mm @ 6 GHz 2019 Wei L. [11] Si/AlN 1.47 dB/mm @ 6 GHz 2020 Ghosh S. [31] Si/AlN…”