High Thermal Conductivity Substrates Research Articles

Simulation investigation of effects of substrate and thermal boundary resistance on performances of AlGaN/GaN HEMTs

The temperature distributions and thermal resistances of the GaN HEMTs fabricated on different substrates (sapphire, Si, SiC and diamond) with Mo/Au interlayers were calculated and analyzed by numerical simulation. The results show that the GaN HEMT on the diamond substrate exhibits the lowest channel temperature and thermal resistance, and the thermal resistance rises with the increase of the thermal boundary resistance (TBR) for all the GaN HEMTs with the different substrate materials. Meanwhile, the high TBR (2 × 10−7 m2·K/W) severely hinders the heat exchange between the GaN layer and the substrate, which makes it difficult for the heat flux to pass through the barrier. Even diamond with high thermal conductivity can hardly reduce the channel temperature of the device. Therefore, TBR must be reduced so that the heat flux can be dissipated through a high thermal conductivity substrate. In addition, the Mo/Au interlayer generates a lower thermal boundary resistance, which has little effect on the channel temperature, thermal resistance and interfacial temperature discontinuity of GaN HEMTs.

Substrate dependence of the self-heating in lead zirconate titanate (PZT) MEMS actuators

Lead zirconate titanate (PZT) thin films offer advantages in microelectromechanical systems (MEMSs) including large motion, lower drive voltage, and high energy densities. Depending on the application, different substrates are sometimes required. Self-heating occurs in the PZT MEMS due to the energy loss from domain wall motion, which can degrade the device performance and reliability. In this work, the self-heating of PZT thin films on Si and glass and a film released from a substrate were investigated to understand the effect of substrates on the device temperature rise. Nano-particle assisted Raman thermometry was employed to quantify the operational temperature rise of these PZT actuators. The results were validated using a finite element thermal model, where the volumetric heat generation was experimentally determined from the hysteresis loss. While the volumetric heat generation of the PZT films on different substrates was similar, the PZT films on the Si substrate showed a minimal temperature rise due to the effective heat dissipation through the high thermal conductivity substrate. The temperature rise on the released structure is 6.8× higher than that on the glass substrates due to the absence of vertical heat dissipation. The experimental and modeling results show that the thin layer of residual Si remaining after etching plays a crucial role in mitigating the effect of device self-heating. The outcomes of this study suggest that high thermal conductivity passive elastic layers can be used as an effective thermal management solution for PZT-based MEMS actuators.

Strategy to solve the thermal issue of ultra-wide bandgap semiconductor gallium oxide field effect transistor

Gallium Oxide (Ga2O3) holds significant potential for the next generation of electronic devices following SiC and GaN due to its ultra-wide bandgap of approximately 4.5 eV - 4.9 eV and high theoretical critical breakdown field strength of 8 MV/cm. Nonetheless, Ga2O3 has a naturally low thermal conductivity, resulting in limited device output performance and hindering Ga2O3 devices from reaching their full theoretical potential. In this study, we demonstrate that the appropriate thermal management strategy can solve the above challenges. By comparing the thermal control schemes including the Ga2O3 FET devices on the original substrate, the thinned Ga2O3 substrate, the high thermal conductivity substrate, the heat sink packaging, and the flip-chip packaging, it is demonstrated that the flip-chip model is the most effective strategy to improve the heat dissipation performance of the Ga2O3 device. By utilizing the appropriate carrier in flip-chip packaging, the temperature elevation of the device at 2 W/mm power density will be diminished by around 91% in contrast to the initial basic device. Furthermore, the output performance of the device demonstrates significant enhancement. This thermal management technique successfully resolves the severe heat dissipation issue prevalent in Ga2O3 devices and eliminates primary obstacles concerning the industrialization of Ga2O3 RF and power devices.

Current transport mechanism of lateral Schottky barrier diodes on β-Ga2O3/SiC structure with atomic level interface

Heterogeneous integration of β-Ga2O3 on highly thermal conductive SiC substrate by the ion-cutting technique is an effective solution to break the heat-dissipation bottleneck of β-Ga2O3 power electronics. In order to acquire high-quality β-Ga2O3 materials on SiC substrates, it is essential to understand the influence of the ion-cutting process on the current transport in β-Ga2O3 devices and to further optimize the electrical characteristics of the exfoliated β-Ga2O3 materials. In this work, the high quality of β-Ga2O3/SiC structure was constructed by the ion-cutting process, in which an amorphous layer of only 1.2 nm was formed between β-Ga2O3 and SiC. The current transport characteristics of Au/Pt/Ni/β-Ga2O3 Schottky barrier diodes (SBDs) on SiC were systematically investigated. β-Ga2O3 SBDs with a high rectification ratio of 108 were realized on a heterogeneous β-Ga2O3 on-SiC (GaOSiC) substrate. The net carrier concentration of the β-Ga2O3 thin film for GaOSiC substrate was down to about 8% leading to a significantly higher resistivity, compared to the β-Ga2O3 donor wafer, which is attributed to the increase in acceptor-type implantation defects during the ion-cutting process. Furthermore, temperature-dependent current–voltage characteristics suggested that the reverse leakage current was limited by the thermionic emission at a low electric field, while at a high electric field, it was dominated by the Poole–Frenkel emission from E3 deep donors caused by the implantation-induced GaO antisite defects. These results would advance the development of β-Ga2O3 power devices on high thermal conductivity substrate fabricated by ion-cutting technique.

Heterogeneous integrated InP/SiC high-performance multilevel RRAM

With the advent of the Age of Big Data, resistive random-access memory (RRAM) shows considerable potential for next generation nonvolatile storage technologies owing to its simplified structure, high switching speed, and low power consumption. However, mainstream prepared materials, such as oxides and halide perovskite, face critical issues for practical applications such as switching uniformity and long-term environmental stability. In this work, we report that high carrier mobility material indium phosphide (InP) is prepared as an RRAM medium and is directly bonded to the high thermal conductivity substrate silicon carbide (SiC) at 200 °C, overcoming large (14.9%) lattice mismatch. Importantly, the bonding strength reaches 9.3 MPa, and this high-performance stable RRAM exhibits nonvolatile and reliable switching characteristics including stable endurance (200 cycles) and long data retention (2000 s). Moreover, multilevel storage is also available by modulating RESET stop voltages. This work provides broad possibilities for high-performance RRAM with structures based on traditional semiconductors in the field of nonvolatile storage.

Thermal analysis of an α -Ga2O3 MOSFET using micro-Raman spectroscopy

The ultra-wide bandgap (UWBG) energy (∼5.4 eV) of α-phase Ga2O3 offers the potential to achieve higher power switching performance and efficiency than today's power electronic devices. However, a major challenge to the development of the α-Ga2O3 power electronics is overheating, which can degrade the device performance and cause reliability issues. In this study, thermal characterization of an α-Ga2O3 MOSFET was performed using micro-Raman thermometry to understand the device self-heating behavior. The α-Ga2O3 MOSFET exhibits a channel temperature rise that is more than two times higher than that of a GaN high electron mobility transistor (HEMT). This is mainly because of the low thermal conductivity of α-Ga2O3 (11.9 ± 1.0 W/mK at room temperature), which was determined via laser-based pump-probe experiments. A hypothetical device structure was constructed via simulation that transfer-bonds the α-Ga2O3 epitaxial structure over a high thermal conductivity substrate. Modeling results suggest that the device thermal resistance can be reduced to a level comparable to or even better than those of today's GaN HEMTs using this strategy combined with thinning of the α-Ga2O3 buffer layer. The outcomes of this work suggest that device-level thermal management is essential to the successful deployment of UWBG α-Ga2O3 devices.

(Invited) Sub-Bandgap Thermoreflectance Imaging of Ultra-Wide Bandgap Semiconductors

Over the past few decades, wide bandgap semiconductors (WBG) have been used to fabricate high power and high frequency devices. Device structures, such as Gallium Nitride (GaN) High Electron Mobility Transistors (HEMTs), have begun to be implemented in commercial products such as electrical vehicles and laptop power chargers. With the continuous increase in energy demand, however, extremely high voltage (>10 kV) applications are needed to increase the grid resiliency, storage, and transmission efficiency. Ultra-wide bandgap (UWBG) Semiconductors, with bandgaps >4 eV, could potentially be used to overcome this barrier. Pushing the maximum voltage limit of these devices, however, can lead to significant power dissipation and excessive joule heating.Unfortunately, the thermal conductivity of some UWBG semiconductors, such as Gallium Oxide, is inherently low and thus requires both device and package level thermal management. Innovative solutions, such as high thermal conductivity substrates, are required to reduce the active channel temperature and extend the device lifetime and reliability. In order to successfully implement these technologies, accurate measurement of the peak temperature and thermal distribution (both vertical and lateral) is necessary. Depth-averaged vertical temperature gradients have been demonstrated via Raman thermometry but this approach can become significantly time consuming if attempting to perform transient or lateral maps. On the other hand, Transient Thermoreflectance Imaging (TTI) has shown the potential to provide high throughput thermal images with high spatial resolution (100 nm) and temporal resolution (50 ns).Traditionally, TTI has been used to probe the temperature of metals due to their inherent high reflectivity. Nevertheless, recent studies have demonstrated the ability to probe the surface temperature of the semiconductor when using near-bandgap illumination sources. Due to the high bandgap of UWBG semiconductors, the maturity of high transmission UV sources, optics and detectors has not yet been fully developed. This study investigates the applicability of sub-bandgap wavelengths to probe the active channel temperature. The thermal properties of both Gallium Oxide transistors and Transfer Length Method (TLM) structures are investigated using TTI. The accuracy of the channel temperature is assessed by direct comparison to the adjacent metal contact temperature. A finite element model (FEM) is developed to understand the thermal transport in low thermally conductive semiconductors. Finally, a 3D analytical model is used to extract thermal properties such as the thermal conductivity of the thin film layers.Figure a) Optical CCD Image of Gallium Oxide Transfer Length Method (TLM) Structure b) Transient Thermoreflectance Image (TTI) of Gallium Oxide TLM using sub-bandgap illumination wavelength. Figure 1

Investigation of the interface electronic characteristics of β-Ga2O3 (1 0 0)/4H-SiC (0 0 0 1)

Due to lower thermal conductivity of β-Ga2O3, gallium oxide power device based on high thermal conductivity substrates has received extensive attention. As a high thermal conductivity semiconductor material, 4H-SiC is suitable as a substrate to combine with β-Ga2O3 due to its small lattice mismatches. Herein, first principle is utilized to analyze the interfacial geometry structures, formation energy, interface binding energy and the electronic properties of the bonding mechanism at different β-Ga2O3 (100)/4H-SiC (0001) interfacial models. The interface formation energy and interface binding energy of β-Ga2O3 (100)/4H-SiC (0001) heterointerfaces are studied by using first principles. The results show that six different β-Ga2O3 (100)/4H-SiC (0001) heterostructures can be stable. Among the six interface models, Si-O interface possesses the smallest values of interface formation energy and interface binding energy after geometry relaxation, indicating highest thermodynamic stability. The differential charge density, bader charge, electron local function and partial density of states (PDOS) of β-Ga2O3 (100)/4H-SiC (0001) interface models are comprehensively investigated to understand the interfacial bonding strength and stability. It is shown that electrons are mainly transferred from the 4H-SiC side to the β-Ga2O3 side. Compared to other interface models, Si-O models, Si-GaO models can form strong Si-O chemical bond at the interface, while the interaction between the C-O models and C-GaO models forms a C-O bond with covalent bond properties.

Transient characteristics of β-Ga2O3 nanomembrane Schottky barrier diodes on various substrates

In this paper, transient delayed rise and fall times for beta gallium oxide (β-Ga2O3) nanomembrane (NM) Schottky barrier diodes (SBDs) formed on four different substrates (diamond, Si, sapphire, and polyimide) were measured using a sub-micron second resolution time-resolved electrical measurement system under different temperature conditions. The devices exhibited noticeably less-delayed turn on/turn off transient time when β-Ga2O3 NM SBDs were built on a high thermal conductive (high-k) substrate. Furthermore, a relationship between the β-Ga2O3 NM thicknesses under different temperature conditions and their transient characteristics were systematically investigated and verified it using a multiphysics simulator. Overall, our results revealed the impact of various substrates with different thermal properties and different β-Ga2O3 NM thicknesses on the performance of β-Ga2O3 NM-based devices. Thus, the high-k substrate integration strategy will help design future β-Ga2O3-based devices by maximizing heat dissipation from the β-Ga2O3 layer.

(Invited, Digital Presentation) Thermal Conductance across Heterogeneously Integrated Interfaces for Thermal Management of Wide and Ultra-Wide Bandgap Electronics

Thermal management is important for wide and ultra-wide bandgap power electronics because overheating degrades device reliability and performance. High thermal conductivity substrates such as SiC and diamond facilitate heat dissipation of these devices while the thermal boundary resistance between devices and substrates accounts for a large portion of the total thermal resistance, which prevents devices from taking the full advantage of the high thermal conductivity of the substrates. Recently, heterogeneously integrated wide and ultra-wide bandgap semiconductor interfaces are found to have low thermal boundary resistances, which provides a new degree of freedom to design and fabricate thermally conductive interfaces for thermal management of related power devices. For example, GaN can be bonded with single crystal SiC or single crystal diamond directly at room temperature. β-Ga2O3 can be bonded with SiC with or without Al2O3 interfacial layers. Compared with growth, the bonded interfaces are not limited by lattice mismatch. Moreover, the room-temperature bonding process discussed in this talk can possibly eliminate the effects of thermal stress existed in high temperature growth or bonding techniques. Recent progresses in this sub-area will be discussed in this talk, especially thermal conductance across surface-activated bonded GaN and β-Ga2O3 interfaces measured by time-domain thermoreflectance (TDTR) and the effects of thermal boundary resistance values on device temperatures. Finally, the potential challenges will also be pointed out, for instance, high-throughput thermal measurements of buried interfaces, thermal property-structure relations of interfaces bonded under different conditions, theoretical understanding of interfacial thermal transport, and device demonstrations.

Laser speckle reduction via TiO2‐sapphire composite rotating wheel in laser projection

AbstractLaser sources have been considered to be better light sources compared to traditional lamps or light‐emitting diodes used in projectors, which enables the projector to create images with higher color saturation, brightness, and energy efficiency. However, the speckle noise caused by the coherent nature of the laser is a major technology obstacle for laser projection, which severely affects the image quality. To suppress laser speckle, a TiO2‐sapphire composite (TSC) with rough and high reflectivity surface and high thermal conductivity substrate is designed, which reduces the laser speckle by creating spatial diversity. Moreover, combined with a micro motor, the design and fabrication of the TSC rotating wheel are realized, which further reduces the laser speckle by creating time diversity. The experimental results show that the laser speckle contrast can be reduced from 9.0% to 2.2% when placing the TSC rotating wheel in the light path, which is below the speckle perception limit of the human eye (<4%). This new type of laser speckle suppression device is simple to use, low in cost, high in energy utilization, high in thermal conductivity, easy to mass production, and has great application potential in high‐power laser projection.

Tip enrichment surface-enhanced Raman scattering based on the partial Leidenfrost phenomenon for the ultrasensitive nanosensors

Surface-enhanced Raman scattering (SERS) possesses the advantage that directly detects target analytes in solution with high specificity and sensitivity without complicated pretreatment procedures. It remains a challenge in most practical applications to achieve molecule sensitivity in any highly diluted solutions. Here, we develop a robust and practical molecular enrichment strategy that can effectively confine analyte molecules and Au nanoparticles together in a short time into a small-sized sensitive region on a needle tip, based on the Leidenfrost phenomenon and capillary force. In this strategy, the Leidenfrost evaporation phenomenon maintains the analytes droplet in a Cassie state based on a levitating force, and at the same time, a hung needle tip anchors the droplet based on the capillary force. After 1–2 min quick evaporation, more than 98% Au nanoparticles and analytes can be condensed into an around 0.5 mm small size area on the needle tip. Due to the significant enrichment capability and reproducibility, the SERS measurement enables to achieve the limit of detection (LOD) down to 0.08 nM (at an S/N ratio of 3) for crystal violet (CV) molecules and to nM level for several types of pesticide molecules (glyphosate, carbendazim, thiram and choline) in ethanol solution. The strategy was also applied to the detection of CV molecules in mixture pigments solution, thiram in spiked environment water samples, with good selectivity and sensitivity. In addition, using the high thermal conductivity substrate without additional surface modification, this enrichment SERS detection may open the possibility of universal applications due to its facile and cost-effective. The accurate site of the needle tip offers great practical potentials for on-site identification by using a handheld Raman spectrometer.

(Invited) Materials Integration, Interlayers, and Interactions for Thermal Management of Wide Bandgap Device Structures

Wide bandgap semiconductor materials provide opportunities for high power device structures and circuits to perform more efficiently than is achievable with silicon. To optimize such performance, however, management of heat dissipation from the device-active regions of the structure is necessary. This presentation will focus on materials integration schemes and on interfacial materials reactions in order to understand thermal transport across interfaces to improve thermal management and hence device performance.Bonding a wide bandgap material to a high thermal conductivity substrate has often been touted as a means to improve thermal conductivity. We will discuss different bonding methods for a variety of materials combinations, including GaN / Si and b-Ga2O3 / SiC and how these results point to opportunities with other materials combinations. As was the case with the development of silicon-on-insulator, these bonding schemes also require the ability to produce structures that include a thin layer of the wide bandgap material on the high thermal conductivity substrate, through a combination of wafer removal and surface polishing. We will demonstrate stock wafer removal or exfoliation combined with chemical-mechanical polishing to achieve such structures. Bonding also requires high quality substrates and our efforts to assess wafer quality prior to bonding using x-ray diffraction and x-ray topography will be described.Interfacial layers and metal contacts can either enhance or degrade thermal transport across interfaces. We will highlight a case where such interlayers improve performance and will also address interactions between deposited metals and the wide bandgap materials and the impact of such interactions on thermal management.

Semi-quantitative orientation control of graphite nanoplatelets in GNP/PU nanocomposite via balancing the effects of gravity and micro-flow field and application in manufacturing heat spreader substrate with excellent thermal conductivity

As the huge demand for a multifunctional electronic device with high performance, an important technology in next-generation electronics is thermal management and there are numerous uses for it in enhancing the reliability and sustainable utilization. In this work, a high thermal conductivity substrate based on graphite nanoplatelets (GNPs)/ polyurethane (PU) nanocomposite film is fabricated. The GNPs’ orientation can be semi-quantitative controlled by balancing the effect of gravity and micro-flow field, which results in a thermal conductivity varies from 38.1 W (m·K)-1 to 19.8 W (m·K)-1 as the orientation rearrangement. Meanwhile, Interfacial thermal resistance is evaluated by the Effective medium theory (EMT) models, which is about 1.76 × 10-6 K m2/W to 2.0 × 10-6 K m2/W at 30 °C. Additionally, the chip fixed to the GNP/PU substrate (38.1 W (m·K)-1) could work under a lower temperature than the commercial polycarbonate substrate. Our method is a promising strategy for thermal management of next-generation electronics devices.

Channel Properties of Ga₂O₃-on-SiC MOSFETs

We report the characterization of the channel mobility properties of metal-oxide-semiconductor field-effect transistors (MOSFETs) on the heterogeneous $\beta $ -Ga2O3-on-SiC (GaOSiC) substrate fabricated by an ion-cutting process. The mobility of GaOSiC MOSFETs is significantly improved as the postannealing temperature of Ga2O3 channel increases from 900 °C to 1200 °C. The GaOSiC transistor annealed at 1200 °C exhibits mobility consistent with the $\beta $ -Ga2O3 donor wafer, which suggests that the defects in Ga2O3 channel induced by the H+ implantation for the ion-cutting step can be eliminated by the high-temperature annealing. As the ambient temperature ( ${T} _{{\mathrm {amb}}}$ ) increases from 0 °C to 150 °C, the mobility within the accumulation regime of GaOSiC MOSFETs decreases with the temperature following a ${T}_{{\mathrm {amb}}}^{-1}$ law, which is limited by the phonon scattering. The results of this work will be critically important for designing the transport properties of the GaOSiC channel, significantly advancing the development of Ga2O3 power devices on high thermal conductivity substrate.

(Invited) Heterogeneous Integration of GaN and Ga2O3 with High Thermal Conductivity Substrates Via Surface Activated Bonding

The high-power high-frequency devices of both GaN and Ga2O3 needs careful thermal management to migrate the self-heating effect during operation. One promising strategy is to integrate GaN and Ga2O3 with a high thermal conductivity substrate such as SiC and diamond. Epitaxial growth, usually at high temperature, met many challenges because of the lattice mismatch and thermal expansion mismatch. Recently, we realized room-temperature bonding of GaN and Ga2O3 with high thermal conductivity substrates via surface activated bonding methods, which can avoid the transition layer necessary for growth method and make the GaN or Ga2O3 device close to the high thermal conductivity substrates as much as possible.

Heteroepitaxial growth of β-Ga2O3 films on SiC via molecular beam epitaxy

β-Ga2O3 is a promising ultrawide bandgap semiconductor for next generation radio frequency electronics. However, its low thermal conductivity and inherent thermal resistance provide additional challenges in managing the thermal response of β-Ga2O3 electronics, limiting its power performance. In this paper, we report the heteroepitaxial growth of β-Ga2O3 films on high thermal conductivity 4H-SiC substrates by molecular beam epitaxy (MBE) at 650 °C. Optimized MBE growth conditions were first determined on sapphire substrates and then used to grow β-Ga2O3 on 4H-SiC. X-ray diffraction measurements showed single phase (2¯01) β-Ga2O3 on (0001) SiC substrates, which was also confirmed by TEM measurements. These thin films are electrically insulating with a (4¯02) peak rocking curve full-width-at-half-maximum of 694 arc sec and root mean square surface roughness of ∼2.5 nm. Broad emission bands observed in the luminescence spectra, acquired in the spectral region between near infrared and deep ultraviolet, have been attributed to donor-acceptor pair transitions possibly related to Ga vacancies and its complex with O vacancies. The thermal conductivity of an 81 nm thick Ga2O3 layer on 4H-SiC was determined to be 3.1 ± 0.5 W/m K, while the measured thermal boundary conductance (TBC) of the Ga2O3/SiC interface is 140 ± 60 MW/m2 K. This high TBC value enables the integration of thin β-Ga2O3 layers with high thermal conductivity substrates to meliorate thermal dissipation and improve device thermal management.

The effect of the substrate on the damage threshold of gold nano-antennas by a femtosecond laser

Gold nano-antennas with silica substrate may not be suitable for high power applications such as heat resisted magnetic recording, solar thermophotovoltaics, and nano-scale heat transfer systems. When a laser beam reaches to these nano-antennas, part of the light is absorbed by the metallic regions, leading to a temperature rise of the device. If these devices reach a temperature beyond its Tamman temperature (the temperature at which sintering of atoms or molecules start to occur), the antenna can be damaged. One strategy to allow the antenna to work at higher fluences (energy density) is to employ substrates that can quickly carry the heat away from the antennas. In this paper, we show that high thermal conductivity substrates, such as diamond, can allow the antenna to withstand 20 times higher fluence than a low thermal conductivity silica substrate.

(Invited) Characterization of Thermal Effects in Wide Bandgap Semiconductor Materials and Devices

Wide bandgap electronics made from nitrides (e.g., Gallium Nitride (GaN)) and oxides (e.g., Gallium Oxide (Ga2O3)) are currently under development due to their potential to create some of the most advanced RF and power electronic devices in the world. However, the thermal response of these devices under applied electric fields can create large power densities (RF and power electronics) that must be understood. For many of these devices, the electrothermal response plays a strong role in both the acceptable operation or long-term failure and reliability of the devices. Thus, tools that can help elucidate these responses and provide a method to help design better devices is of critical need for this field.In this talk we will discuss advancements in thermal characterization techniques that have allowed new insights into electrothermal behavior in GaN and Ga2O3 materials and devices. Specifically, a focus on the role of device architecture and material processing will be addressed. For GaN and Ga2O3 RF and power electronics, the role of thermal interfaces in the heat dissipation of both lateral and vertical device architectures will be discussed. We will cover aspects of semiconductor-semiconductor as well as metal-semiconductor interfaces and their roles in device thermal management. A highlight will be the use of plasma activated bonding to provide ultralow thermal resistance interfaces that allow for heterogenous integration of nitrides and oxides with high thermal conductivity substrates. Finally, we will discuss the implications of these effects on device behavior through experiments and modeling.

Interfacial Thermal Conductance across Room-Temperature-Bonded GaN/Diamond Interfaces for GaN-on-Diamond Devices.

The wide bandgap, high-breakdown electric field, and high carrier mobility makes GaN an ideal material for high-power and high-frequency electronics applications, such as wireless communication and radar systems. However, the performance and reliability of GaN-based high-electron-mobility transistors (HEMTs) are limited by the high channel temperature induced by Joule heating in the device channel. Integration of GaN with high thermal conductivity substrates can improve the heat extraction from GaN-based HEMTs and lower the operating temperature of the device. However, heterogeneous integration of GaN with diamond substrates presents technical challenges to maximize the heat dissipation potential brought by the ultrahigh thermal conductivity of diamond substrates. In this work, two modified room-temperature surface-activated bonding (SAB) techniques are used to bond GaN and single-crystal diamond. Time-domain thermoreflectance (TDTR) is used to measure the thermal properties from room temperature to 480 K. A relatively large thermal boundary conductance (TBC) of the GaN/diamond interfaces with a ∼4 nm interlayer (∼90 MW/(m2 K)) was observed and material characterization was performed to link the interfacial structure with the TBC. Device modeling shows that the measured TBC of the bonded GaN/diamond interfaces can enable high-power GaN devices by taking full advantage of the ultrahigh thermal conductivity of single-crystal diamond. For the modeled devices, the power density of GaN-on-diamond can reach values ∼2.5 times higher than that of GaN-on-SiC and ∼5.4 times higher than that of GaN-on-Si with a maximum device temperature of 250 °C. Our work sheds light on the potential for room-temperature heterogeneous integration of semiconductors with diamond for applications of electronics cooling, especially for GaN-on-diamond devices.