Si Substrate Removal Research Articles

SiC/Si Hybrid Substrate Synthesized by the Method of Coordinated Substitution of Atoms: A New Type of Substrate for LEDs

This paper proposes a new type of substrate for manufacturing LEDs based on AlInGaN heterostructures. Instead of depositing SiC layers on the surface of Si using the conventional method, a new method involving the coordinated substitution of atoms (MCSA) to form the SiC layer is proposed. This new approach enables the growth of epitaxial GaN layers with low defect content and facilitates transfer to any surface. The paper details the technology of manufacturing LEDs on SiC/Si substrates obtained by the MCSA and elaborates on the benefits of using these substrates in LED production. Additionally, the advantages of the growth interface between SiC and Si materials are discussed. Moreover, it is found that thinner SiC layers (<200 nm) contribute to the scattering of the LED’s own radiation in the heterostructure waveguide, which decreases its absorption by silicon. For flip-chip LEDs with the substrate removed, substrates with thicker SiC layers (~400 nm) and a growth porous layer of several microns at the SiC-Si interface is utilized to simplify Si substrate removal and enhance the manufacturing process’s cost-effectiveness.

High quality of N-polar GaN film fabricated by layer transfer technology using high selective material removal rate of CMP

A new method has been proposed for layer transfer technology to fabricate N-polar GaN film, which is extremely promising to be applied in the preparation of related devices. In our study, after wafer bonding and original Si substrate removal process, the N-polar GaN was exposed by chemical mechanical polishing (CMP) within a short time due to the high selective material removal rate (MRR) ratio of about 35:1 between N-polar AlxGa1-xN (0.33≤x≤1, 1400 nm/min) and N-polar GaN (40 nm/min). The high selective MRR can be attributed to the different corrosion resistance. Hexagonal hillock structure and corrosion pits were appeared quickly on the AlN surface when immersing the N-polar AlN and N-polar GaN in the same CMP slurry, but was not observed on the GaN surface. Meanwhile, the quality of the fabricated N-polar GaN film has been characterized by atomic force microscope (AFM) and Photoluminescence (PL) spectroscopy. Comparing with the N-polar GaN processed through inductive coupled plasma (ICP) etching, the N-polar GaN fabricated by CMP has smaller surface roughness (Rq=0.307 nm) and stronger band-edge PL intensity indicating fewer surface damage. These results can provide guidance on the fabrication of N-polar GaN related devices.

GaN-Based Resonant-Cavity Light-Emitting Diodes Grown on Si.

GaN-on-Si resonant-cavity light-emitting diodes (RCLEDs) have been successfully fabricated through wafer bonding and Si substrate removal. By combining the chemical mechanical polishing technique, we obtained a roughness of about 0.24 nm for a scan area of 5 μm × 5 μm. The double-sided dielectric distributed Bragg reflectors could form a high-quality optical resonant cavity, and the cavity modes exhibited a linewidth of 1 nm at the peak wavelength of around 405 nm, corresponding to a quality factor of 405. High data transmission in free space with an opening in the eye diagram was exhibited at 150 Mbps, which is limited by the detection system. These results showed that GaN-based RCLEDs grown on Si are promising as a low-cost emitter for visible light communications in future.

GaN-on-diamond technology platform: Bonding-free membrane manufacturing process

GaN-on-diamond samples were demonstrated using a membrane-based technology. This was achieved by selective area Si substrate removal of areas of up to 1 cm × 1 cm from a GaN-on-Si wafer, followed by direct growth of a polycrystalline diamond using microwave plasma chemical vapor deposition on etch exposed N-polar AlN epitaxial nucleation layers. Atomic force microscopy and transmission electron microscopy were used to confirm the formation of high quality, void-free AlN/diamond interfaces. The bond between the III-nitride layers and the diamond was validated by strain measurements of the GaN buffer layer. Demonstration of this technology platform is an important step forward for the creation of next generation high power electronic devices.

Optical and Thermal Performances of (Ga,In)N/GaN Light Emitting Diodes Transferred on a Flexible Tape

Blue (Ga,In)N-based light-emitting diodes (LEDs) grown on a Si(111) substrate by metal-organic vapor phase epitaxy are transferred on a flexible tape after the Si substrate removal. Their optical and thermal behaviors are measured and compared to those of regular LEDs on Si. The light output power of the flexible LEDs is increased due to a higher light extraction efficiency related to the removal of the absorbing Si substrate. However, the maximum output power is limited by thermal effects due to the lower thermal conductivity of the flexible tape. Monitoring the electroluminescence wavelength of the flexible LEDs allows determining their acceptable operating range. The maximum flexible LED luminance is 5×10 5 cd/m 2 .

Low Power Thermal Tuning in Resonant Vertical Junction Silicon Modulators Through Substrate Removal

We report on thermally tunable modulators, with efficiencies up to 2.16 nm/mW. Efficient performance was accomplished through integrated heater design and Si substrate removal, where the heavily N+ doped Si heater element is integrated into the body of the microdisk. For comparison, modulators with an external heater design were also tested with small diameter Si substrate removed. The external heavily doped N+Si heater bars were fabricated outside the diameter of the microdisk. Efficiency for external heater design was 0.68 nm/mW with substrate removed. Both types of thermal modulators were experimentally tested and simulated for a complete understanding of the Si substrate's influence on heat dissipation with both types benefiting significantly from substrate removal. Agreement between simulation and experimental results was greater than 80 $\%$ in all instances.

720-V/0.35-m<inline-formula> <tex-math notation="LaTeX">$\Omega \cdot$ </tex-math> </inline-formula>cm2Fully Vertical GaN-on-Si Power Diodes by Selective Removal of Si Substrates and Buffer Layers

This letter demonstrates a novel technology to fabricate fully vertical GaN-on-Si power diodes with state-of-the-art performance. Si substrate and buffer layers were selectively removed and the bottom cathode was formed in the backside trenches extending to an n+-GaN layer. A specific differential ON-resistance of 0.35–0.4 $\text{m}\Omega \cdot $ cm2 (normalized to the total device area) and a breakdown voltage of 720 V were demonstrated in this novel fully vertical GaN-on-Si p-n diode, rendering a Baliga’s figure of merit over 1.5 GW/cm2. These results set a new record performance in all vertical GaN power diodes on foreign substrates, and demonstrate the feasibility of making fully vertical GaN-on-Si power diodes and transistors by selective removal of Si substrates and buffer layers.

GaN-on-silicon high-electron-mobility transistor technology with ultra-low leakage up to 3000 V using local substrate removal and AlN ultra-wide bandgap

We report on extremely low off-state leakage current in AlGaN/GaN-on-silicon metal–insulator–semiconductor high-electron-mobility transistors (MISHEMTs) up to a high blocking voltage. Remarkably low off-state gate and drain leakage currents below 1 µA/mm up to 3 kV have been achieved owing to the use of a thick in situ SiN gate dielectric under the gate, and a local Si substrate removal technique combined with a cost effective 15-µm-thick AlN dielectric layer followed by a Cu deposition. This result establishes a manufacturable state-of-the-art high-voltage GaN-on-silicon power transistors while maintaining a low specific on-resistance of approximately 10 mΩ·cm2.

The investigation of in situ removal of Si substrates for freestanding GaN crystals by HVPE.

We investigate the etching of a Si substrate in the fabrication process of freestanding GaN crystal grown using a Si by HVPE. Followed by crystal growth, Si etching by vapor HCl at high temperature results in successful fabrication of the freestanding GaN. Due to the complicated vertical gas flows inside the reactor, careful design of the susceptor was implemented. The unintentional formation of SixNy thin layer at the backside of the Si substrate after the epitaxial growth, which can cause the decreased etch rate and non-uniform etching of a Si substrate, was successfully prevented by N2 purging during and after the etching of a Si substrate. We believe that this study will guide us to achieve the growth of freestanding GaN over 8-inch diameters in the efficient and practical way.

Demonstration of fully vertical GaN‐on‐Si Schottky diode

The realisation of a fully vertical gallium nitride (GaN)-on-silicon (Si) Schottky barrier diode (SBD) without using wafer bonding and Si substrate removal process is reported. The SBD presented a turn-on voltage of 0.69 V at 1 A/cm 2 , breakdown voltage of 148 V with a specific on-resistance of 13.9 mΩ cm 2 . The ideality factor and Schottky barrier height were 1.35 and 0.71 eV, respectively. An effective critical electric field was estimated to be 1.48 MV/cm. The Baliga's figure of merit for the SBD was calculated to be 1.57 MW/cm 2 . These results indicate the great potential of GaN-on-Si in achieving cost-effective fully vertical power device.

In brief

PAGE 1596 Researchers in France and Germany have developed a GaAs-based Fabry-Pérot cavity photoconductor designed for sub-sampling radio frequencies and sub-THz waves. The GaAs layer is grown at low temperature and photoconductive response is triggered by a 1550 nm pulsed laser. The photoconductor paves the way for analogue-to-digital signal conversion in ultrafast optoelectronics. PAGE 1598 A fully-vertical GaN-on-silicon Schottky barrier diode (SBD) is presented in work from Japan. The SBD is made without using wafer bonding or Si substrate removal processes to realise a device with high breakdown voltages and efficient thermal management. Reported electronic properties of the diode demonstrate it to be a cost-effective and energy efficient power device. A low-temperature-GaAs photoconductor controlled by a 1550 nm mode-locked laser PAGE 1578 A sensor for accurate fatigue failure detection in ferromagnetic materials is proposed in work from China. The pick-up coil of the designed sensor is attached by a spring to reduce lift-off events-reducing errors in surface contact and measurements. Voltage signals between the pick-up coil and material surface are used to accurately assess structural damage and stress in ferromagnetic materials. Fabrication of a cost effective and energy efficient fully-vertical GaN-on-silicon Schottky diode PAGE 1606 A geosynchronous synthetic aperture radar (GEO-SAR) system is used to realise time-variant total electron count (TEC) real-time measurements in work from the UK and China. The process is reported to be much simpler than conventional ionospheric sounding methods for estimating TEC with advantages including higher measuring accuracy, no requirement for atmospheric sounding equipment and superior compensation for ionospheric effects. Accurate fatigue detection in ferromagnetic materials with a sensor reduce lift-off events PAGE 1576 Researchers from China report a stopping criterion for belief propagation (BP) decoding of polar codes. The criterion uses the frozen bit error rate to prevent unnecessary computational iterations during decoding. Simulation results show that this approach can be used to determine if a polar code has been successfully decoded with a lower computational complexity than previously reported methods. Using geosynchronous synthetic aperture radar for the accurate measurement of real-time total electron count A stopping criteria for belief propagation based on the frozen bit error rate is proposed for polar code decoding

The investigation of stress in freestanding GaN crystals grown from Si substrates by HVPE

We investigate the stress evolution of 400 µm-thick freestanding GaN crystals grown from Si substrates by hydride vapour phase epitaxy (HVPE) and the in situ removal of Si substrates. The stress generated in growing GaN can be tuned by varying the thickness of the MOCVD AlGaN/AlN buffer layers. Micro Raman analysis shows the presence of slight tensile stress in the freestanding GaN crystals and no stress accumulation in HVPE GaN layers during the growth. Additionally, it is demonstrated that the residual tensile stress in HVPE GaN is caused only by elastic stress arising from the crystal quality difference between Ga- and N-face GaN. TEM analysis revealed that the dislocations in freestanding GaN crystals have high inclination angles that are attributed to the stress relaxation of the crystals. We believe that the understanding and characterization on the structural properties of the freestanding GaN crystals will help us to use these crystals for high-performance opto-electronic devices.

Three-Layered Stacking Process by Au/SiO2 Hybrid Bonding for 3D Structured Image Sensors

In this study, a 3D structured CMOS image sensor that can process signals pixelwise in parallel is investigated as a means to simultaneously increase the pixel count and frame rate. To enhance sensor performance beyond current technologies, higher integration via multilayer stacking is essential. We developed a multilayering technique based on repetitive Au electrode embedding, direct bonding, and Si substrate removal processes. To this end, we fabricated a three-layered daisy-chain test device with 6-μm-pitch Au electrodes. Experimental results show that the series of electrical interconnections exceeds 986,000 contacts with an Au contact resistance of ~92.8 mΩ for a single connection.

Fully Vertical GaN p-i-n Diodes Using GaN-on-Si Epilayers

Using GaN-on-Si epilayers, for the first time, fully vertical p-i-n diodes are demonstrated after Si substrate removal, transfer, and n-electrode formation at the top of the device. After SiO2 sidewall passivation, the vertical p-i-n diodes, with n-GaN facing up, exhibit $V_{{\mathrm{\scriptscriptstyle ON}}}$ of 3.35 V at 1 A/cm2, a low differential on-resistance of 3.3 $\text{m}\Omega $ cm2 at 300 A/cm2, and a breakdown voltage of 350 V. The corresponding Baliga's figure of merit is 37.0 MW/cm2, a very good value for GaN-based p-i-n rectifiers grown on Si substrates. The results indicate that fully vertical rectifiers using GaN-on-Si epilayers have great potential in achieving cost-effective GaN devices for high-power and high-voltage applications.

Thermally Engineered Flip-Chip InGaN/GaN Well-Ordered Nanocolumn Array LEDs

Thermally engineered flip-chip (FC) InGaN/GaN well-ordered nanocolumn array light-emitting diodes (LEDs) are demonstrated for the first time. A directional photoluminescence beam profile was observed from the n-side bottom of the GaN nanocolumns, which maintained an optically damage-free periodic arrangement of nanocolumns through the FC process involving Si substrate removal by wet etching. The developed LED achieved single-peak emission at $\sim 570$ nm in the middle of the visible range. The thermal resistance of the nanocolumn LED was significantly reduced using the FC configuration.

Flip‐chip bonding and fabrication of well‐ordered nanocolumn arrays on sputter‐deposited AlN/Si (111) substrate

Employing a thin AlN film sputter‐deposited on Si substrates, well‐ordered GaN nanocolumn arrays were demonstrated by RF‐plasma‐assisted molecular‐beam‐epitaxy selective‐area growth. Dislocation‐free crystals were grown even on this cost‐effective framework, which included high‐density threading dislocations (>3 × 1011 cm−2), by applying nanocolumn growth techniques. Single‐peak PL spectra from integrated InGaN/GaN MQW were obtained in red region and the peak wavelength changed from 640 to 690 nm with increasing nanocolumn diameter. This framework also contributes to a fabrication of vertical injection type flip‐chip structure, even if a nanocolumn device. Damage‐free wet‐etching removal of Si substrates resulted in exposure of flip‐chip well‐ordered nanocolumns array.(a) TEM image of nanocolumns array on sputter‐deposited thin AlN film/Si (111) substrate. (b) SEM image of flip‐chip well‐ordered nanocolumns array.

High‐efficiency blue and green LEDs grown on Si with 5 micrometer thick GaN buffer

AbstractHigh‐efficiency blue and green light‐emitting diodes (LEDs) were grown on planar Si substrates using a 5 µm thick GaN buffer by metalorganic chemical vapor deposition (MOCVD). AlN/GaN superlattices (SLs)–based interlayers were inserted twice for stress balancing and dislocation reduction. Smooth surface and low dislocation density of 1 × 109 cm–2 were achieved. The light output power (LOP) of bare 300 × 300 µm2 447 nm–LEDs and 510 nm–LEDs on Si was measured to be 2.15 mW and 0.85 mW at 20 mA, respectively. At –15 V, leakage current of as low as 3 µA was achieved for 447 nm–LEDs while higher leakage current was measured for green LEDs. After Si substrate removal, the LOP of packaged 440 nm– and 500 nm–LEDs reached 8.50 mW and 4.85 mW at 20 mA, respectively. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Significant enhancement of breakdown voltage for GaN DHFETs by Si substrate removal

AbstractIn this paper, we present a study on the substrate removal of AlGaN/GaN/AlGaN double‐heterostructure FETs (DHFETs) on Si (111) substrates by 2 different approaches: a global versus local removal route. We report on the significant enhancement of breakdown voltage (VBD) of DHFETs with only 2 µm thick AlGaN buffer in both cases. In the case of global Si removal, the Si substrate is completely removed and transferred to the sapphire carrier. However, for the local Si removal, the Si substrate is selectively etched only under the source‐to‐drain regions. Before Si removal, VBD saturates at ∼ 700 V at a gate‐drain distance (LGD) ≥ 8 µm: confirming electrical breakdown into the Si substrate. The breakdown voltage is remarkably enhanced after etching away the substrate by either of the techniques. We measure a VBD > 1100 V for devices with LGD ≥ 15 µm with a buffer thickness of only a 2 µm (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Experimental and simulation study of breakdown voltage enhancement of AlGaN/GaN heterostructures by Si substrate removal

The breakdown mechanism in GaN-based heterostructures (HFETs) grown on silicon substrate is investigated in detail by TCAD simulations and silicon substrate removal technique. High-voltage electrical measurements show that the breakdown voltage saturates for larger gate-drain distances. This failure mechanism is dominated by the avalanche breakdown in the Si substrate. High-voltage TCAD simulations of AlGaN/GaN/Si substrate structures show higher impact ionization factor and electron density at the Si interface indicating a leakage current path where avalanche breakdown occurs. Experimentally, by etching off the Si substrate the breakdown voltage no longer saturates and linearly increases for all gate-drain gaps. We propose the silicon removal technique as a viable way to enhance the breakdown voltage of AlGaN/GaN devices grown on Si substrate.