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Efficiency and privacy-preserving are two key requirements in developing computing systems for processing of privacy-related information. Here, we experimentally demonstrate one AlGaN/GaN high-electron-mobility transistor (HEMT) one Au/NbOx/HfO2/Pt memristor (1HT1R) structure, which features sub-8ns latency, < 96 fJ programming energy, 104s retention at 85 °C and endurance of >106 cycles. We further build a hardware encryptor by combining HEMT-implemented XOR gate and a true random number generator (TRNG) based on variation in Pt/SiOx:Ag/Pt memristor. The proposed TRNG is able to generate 0.48Mb random bitstreams with ultralow energy consumption of 50fJ/bit. A memristors-based homomorphic encryption system is thus constructed based on the 1HT1R and hardware encryptor, capable of performing image segmentation with ultrafast speed, low energy consumption, and privacy-preserving capability. [ABSTRACT FROM AUTHOR]

This article investigates the displacement damage on AlGaN/GaN high-electron-mobility transistors (HEMTs) using the 30-MeV fluorine ions. The electrical degradation and the defects in HEMTs were examined before and after irradiation. Three defect states are detected in a deep-level transient analysis system (DLTS), including a broad surface state peak ($N_{1}$) and two bulk defect peaks ($H_{1}$ and $H_{2}$). The energy levels of these two defects are $E_{\mathrm {C}} 0.63$ eV ($H_{2}$) and $E_{\mathrm {C}} 0.91$ eV ($H_{1}$), respectively. There is a linear relationship between the concentration of $H_{1}$ and the fluorine ion fluence. The radiation damage and electrical performance degradation of AlGaN/GaN HEMTs are simulated by combining with simulation software of different methods. The calculated results are in agreement with the experimental data. The performance degradation caused by heavy ion of the device is mainly caused by the $H_{1}$ defect. The effect of defects with shallow energy level is shielded by the Fermi-level pinning in deeper energy level. Moreover, the defect distribution of GaN in AlGaN/GaN heterojunction plays a major role. It is found that the method of combining experimental data with multiscale simulation is an effective way to predict the radiation damage of devices. [ABSTRACT FROM AUTHOR]

The combined effects of proton irradiation and forward gate-bias stress on the interface traps of AlGaN/GaN heterostructure have been studied in this article. It is found that the effect of proton irradiation and forward gate-bias on the shift of flat band voltage $V_{\mathrm {FB}}$ is independent. By utilizing the frequency-dependent conductance technique, it is found that the trap density $D_{\mathrm {T}}$ at metal/AlGaN interface decreases after proton irradiation and the $D_{\mathrm {T}}$ at most energy levels increases after the following forward gate-bias. The $D_{\mathrm {T}}$ at AlGaN/GaN interface increases after proton irradiation and then decreases after the following forward gate-bias. The energy level range of metal/AlGaN interface traps reduces significantly under the forward gate-bias for the irradiated devices, however, that of AlGaN/GaN interface traps decreases little. In summary, the combined effect of proton irradiation and forward gate-bias stress on the interface traps is more complex than that on the bulk traps in AlGaN layer. [ABSTRACT FROM AUTHOR]

To explore the role of hydrogen in radiation degradation of AlGaN/GaN high-electron-mobility transistors (HEMTs), the performance degradation of the hydrogen untreated and pretreated devices is compared under the exposure of carbon ions. The energy of carbon ions is chosen as 7.6 MeV, and the maximum fluence reaches 4 × 1012 cm−2. By electrical character measuring, it is found that the positive shift of the threshold voltage and the decrease of the transconductance occur after to the irradiation. Hydrogen pretreatment accelerates the shift of threshold voltage and the decrease of the transconductance. The threshold voltage of the device is almost unchanged under 1-MeV electron irradiations. This means that the displacement damage leads to the shift of the threshold voltage. The height of Schottky barrier hardly changes in the hydrogen pretreated devices, showing that the ionization defects such as the formation of interface states under the gate are not the main cause of device degradation. Deep level transient spectrum (DLTS) results show that the irradiations cause the increase of gallium vacancies, and the hydrogen pretreatment inhibits its formation. According to the first principle calculation, the existence of hydrogen in GaN layer can reduce the formation energy of and the number of charges of the defects. It is speculated that hydrogen atoms participate in the evolution of radiation defects, which changes the types and number of defects in the devices. [ABSTRACT FROM AUTHOR]

The electrical degradation in AlGaN/GaN high-electron-mobility transistors (HEMTs) is examined under irradiation with 7.6-MeV carbon (C), 20-MeV oxygen (O), and 30-MeV fluorine (F) ions in situ. To characterize the radiation damage in the HEMTs, the ionizing dose Di, displacement dose Dd, and number of vacancies versus the chip depth in the devices have been calculated for heavy ions. As expected, in all three types of HEMTs, the output current decreases more than 30% and threshold voltage positive shifts after the irradiation fluence of 4 × 1012 ions/cm2. The performance degradation of AlGaN/GaN HEMTs is caused by radiation-induced charged defects. Based on calculation and experimental results, it is shown that the nonionizing energy loss (NIEL) method is not suitable for estimating the degradation of AlGaN/GaN HEMTs either considering gallium vacancy or considering both gallium vacancy and nitrogen vacancy. In the same displacement damage dose, the threshold voltage degradation rate depends on the type of incident particles and independent of the channel length. The damage caused by carbon ions is the smallest and the damage caused by fluoride ions is the largest. [ABSTRACT FROM AUTHOR]

The effect of gamma (γ)-irradiation on AlGaN-based light-emitting diodes (LEDs) in the short-wavelength ultraviolet (UVC, 210–280 nm) spectral range under electrical stress is characterized by electroluminescence and current–voltage measurement. Different from previous reports that γ-irradiation can hardly damage nitride devices, we observe that the optical power decreases and leakage current increases obviously after electrical stress under γ-irradiation. To delve into the nature of degradation, variation of defects is studied using temperature-dependent low-frequency noise measurement. After stress, the ~0.78-eV defects attributed to N antisite are generated and lead to device degradation, which is accompanied by a reduction of the intrinsic Ga vacancy with an energy level of ~0.38 eV. The variation of defects after stress in γ-irradiated environment is more evident than that in nonirradiated environment, which is well corresponding to the performance degradation behavior. In conclusion, γ-irradiation is found to accelerate degradation induced by electrical stress, and the study can help improve irradiation resistance in AlGaN-based UVC LEDs. [ABSTRACT FROM AUTHOR]

In this article, the C – V curve shift, trap densities responsiveness, and dynamic RON of AlGaN/GaN/GaN:C (SH:C) and AlGaN/GaN/graded-AlGaN:Si/GaN:C (DH:Si/C) heterostructure Schottky barrier diodes (SBDs) have been systematically analyzed. Due to additional 3-D electrons in graded-AlGaN:Si layer, the composite 2-D–3-D channel of DH:Si/C has a higher carrier concentration. Reducing the OFF-state electric field strength through AlGaN:Si insert layer, a smaller positive shift of C – V curve is achieved under OFF-state stress. Due to the charge shielding effect of AlGaN:Si insert layer, trapping/detrapping effects in GaN:C buffer under the OFF-state stress are well suppressed. Compared with SH:C heterostructure, the trap density responsiveness of DH:Si/C heterostructure under OFF-state stress is significantly reduced. At the same time, trap density responsiveness of the upper channel is immune to OFF-state electric stress time. In addition, the proposed SBDs show lower ON-resistance with on reverse bias stress and better dynamic performance with on reverse stress time. [ABSTRACT FROM AUTHOR]

In order to further improve the electrical characteristics of AlGaN-buffer devices, we propose a new in situ SiN/AlGaN-sandwich-barrier (SWB)/GaN/Al0.05GaN high-electron mobility transistors (HEMTs). The dc, channel temperature, and RF temperature of the proposed AlGaN-buffer devices have been systematically studied and analyzed. The SWB structure can effectively reduce the peak value of the electric field, thus effectively reducing the self-heating effect and improving the breakdown characteristics. Through the channel temperature extraction method of pulsed IV and TCAD thermal simulation, the channel temperature of devices with different barrier structures is compared and analyzed, which proves that SWB structure can effectively reduce the channel temperature of devices. Due to the more obvious potential modulation effect between gate and drain, the ƒmax of device can improve more effectively with the increase of drain voltage. In addition, load-pull measurement at 10 GHz revealed that a saturated power density increased from 7.3 to 8.4 W/mm and an associated PAE increased from 24.9% to 29.4%. [ABSTRACT FROM AUTHOR]

The AlGaN/GaN high-electron mobility transistors (HEMTs) were irradiated with fast and thermal neutrons at various fluences. Output, transfer, and gate-leakage characteristics were analyzed in detail before and after irradiation. After irradiation by 14-MeV neutrons, the electrical characteristics of the devices gradually degraded as the fluence increased. After irradiation by thermal neutrons at a fluence of $2.12 \times 10^{16}$ cm−2, the electrical characteristics of devices significantly decreased. Neutrons are believed to introduce a negatively charged acceptorlike deep level in the AlGaN layer, which can deplete 2DEG in the channel, raise the energy band, and shift the threshold voltage to positive values. Such an enhanced barrier can significantly suppress the gate Schottky leakage current of AlGaN/GaN HEMTs in both the reverse and forward bias regions. After the thermal neutron radiation, the quality of Schottky contacts deteriorated significantly. [ABSTRACT FROM AUTHOR]

This paper reports the AlGaN/GaN/ Si $\delta $ -doped AlGaN/GaN:C HEMT device on silicon with high channel conductivity, high breakdown field (E-field) strength, and low current collapse by using the Si-doped AlGaN back barriers. The Si $\delta $ -doped AlGaN back barrier was used to compensate for the reduction of channel conductivity as a result of a carbon-doped semiinsulating GaN buffer layer. The maximum drain current increases from 412 to 720 mA/mm, and peak extrinsic transconductance is improved from 103 to 210 mS/mm. Due to the reduction of electric field between the gate and drain along the GaN channel by inserting the Si $\delta $ -doped AlGaN back barrier layer, it can effectively suppress the capture of electrons in channel by carbon-induced accepted traps in the GaN:C buffer. Combined with the high conductivity of Si $\delta $ -doped AlGaN back barrier and high resistance of GaN:C buffer, the device showed the high breakdown E-field strength and the low specific on-resistance. Our proposed device is observed to hold a gate–drain voltage of 769 V at $\textsf {10}~\mu \text{A}$ /mm (7- $\mu \text{m}$ gate–drain spacing) and 0.53 $\text{m}\Omega ~\cdot $ cm $^{{2}}$ and the gate-to-drain electric field corresponds to 1.1 MV/cm. [ABSTRACT FROM AUTHOR]

High performance enhancement-mode (E-mode) AlGaN/GaN high electron mobility transistors (HEMTs) were achieved by using the TiN-based source contact ledge and two-step fluorine treatment. Due to the effective reduction of the source resistance by TiN-based source contact ledge, the peak extrinsic trans-conductance improved by 21.2% from 340 to 412 mS/mm. In addition, due to the enhancement of the back barrier by the two-step fluorine treatment, the three-terminal OFF-state breakdown voltage (BVDS) improved by 11.5% from 162 to 183 V. The proposed E-mode AlGaN/GaN HEMTs exhibit a maximum drain current of 845 mA/mm (@ ${V} _{\text {GS}} =3$ V), a threshold voltage (${V} _{\text {th}}$) of 0.6 V, a high current-gain cutoff frequency ${f} _{\text {T}}$ of 61 GHz, and a high power-gain cutoff frequency ${f} _{\text {MAX}}$ of 130 GHz. Approximately 5% current collapse occurs at a drain quiescent bias of 30 V. The calculated Johnson’s figure of merit (J-FOM = $\text{BV}_{\text {DS}}\times {f}_{T}$) is 11.2 THz-V, the highest so far for GaN-based HEMTs. The calculated $\text {BV}_{\text {DS}} \times {f}_{\text {MAX}}$ value is 23.8 THz-V, indicating significantly improved the speed and power performance of the E-mode GaN-based HEMT. [ABSTRACT FROM AUTHOR]

This paper provides a systematic study on the bulk traps and interface states in a typical AlGaN/GaN Schottky structure under proton irradiation. After 3 MeV proton irradiation with a dose of 5 × 1014 H+/cm2, a positive flat band voltage shift of 0.3 V is observed according to the capacitance-voltage (C-V) measurements. Based on this, the distribution of electrons across AlGaN and GaN layers is extracted. Associated with the numerical calculation, direct experimental evidences demonstrate that the bulk traps within the AlGaN layer dominate the carrier removal effect under proton irradiation. Furthermore, the effects of proton irradiation on AlGaN/GaN interface states were investigated by utilizing the frequency dependent conductance technique. The time constants are extracted, which increase from 1.10–2.53 μs to 3.46–37 μs after irradiation. Meanwhile, it shows that the density of interface states increases from 9.45 × 1011–1.70 × 1013 cm−2·eV−1 to 1.8 × 1012–1.8 × 1013 cm−2·eV−1 with an increase in trap activation energy from 0.34 eV–0.32 eV to 0.41 eV–0.35 eV after irradiation. The Coulomb scattering effect of electron trapping at interface states with deeper energy levels is utilized to explain the mobility degradation in this paper. [ABSTRACT FROM AUTHOR]

A high combination of transconductance ( \textg\text {m} ), current gain cutoff frequency ( \textf\text T ) and three terminal breakdown voltage was achieved using thin barrier AlGaN/GaN HEMTs and TiN-based source contact ledge. The sheet resistance is effectively reduced, whereas the peak extrinsic trans-conductance is improved by 24% from 334 to 415 mS/mm. The thin barrier AlGaN/GaN HEMTs with TiN-based source ledge exhibit a maximum drain current of 1096 mA/mm, a three-terminal off-state breakdown voltage (BV \textsf {DS} ) of 151 V, a high current-gain cutoff frequency \textf\text T of 69 GHz, and a high power-gain cutoff frequency \textf\text {MAX} of 110 GHz. No significant drain current collapse was observed on thin barrier AlGaN/GaN HEMTs with TiN-based source contact ledge. The uniform \textf\text T characteristic over a wide range of bias condition is achieved by using the TiN-based source contact ledge devices. The calculated Johnson’s figures of merit (J-FOM = BV \textsf {GD}\times \text{f}\text T ) is 10.4 THz-V, which is the highest record so far for 0.2\mu \textm T-gate SiN passivation AlGaN/GaN HEMTs without source field plate. [ABSTRACT FROM AUTHOR]

The subthreshold characteristic of gate-recessed high-electron-mobility transistors (HEMTs) using dual-gate (DG) architectures is systematically studied. The recessed DG structure can effectively shift the threshold voltage ( V\text {th} ) in the positive direction. Different from the complex function expression between V\text {th} and AlGaN thickness ( \texttb ) in the recessed single-gate (SG) device, the variation of \textV\text {th} with tb is monotonic in the recessed DG devices. Recessed DG device exhibits a low off-state leakage current of \sim 3\times 10^-10 A/mm and gate induced drain leakage is effectively improved. A higher I \mathrm{\scriptscriptstyle ON}/I \mathrm{\scriptscriptstyle OFF} range of recessed DG devices broadens about 2 times and provide a wider range of tb than that of recessed SG devices. The DG structure has a stronger modulation effect on drain–source resistance ( R\text {ds} ) and gate–drain resistance ( R\text {gd} ) than the SG devices. A lower subthreshold swing (SS) of ~100 mV/dec is obtained by recessed DG design. Due to the second gate inducing the lateral extension of depletion region between the first gate and drain, the off-state leakage and first gate reverse leakage have been significantly improved. Therefore, the recessed DG architecture design can effectively improve the fluctuation of SS and off-state current versus the different AlGaN barrier thickness. [ABSTRACT FROM PUBLISHER]

AlGaN/AlN/GaN heterojunctions were irradiated by 3 MeV protons with different fluences. Hall and C-V measurements showed that the density and mobility of 2DEG for heterojunctions decreased after proton irradiation. The crystal quality and optical properties of AlGaN/GaN heterojunctions were characterized by the variations of the micro-Raman scattering spectra, XRD and photo luminescence (PL) spectra with proton fluence. It has been obtained that the strain and dislocation of GaN and AlGaN were not affected by the proton injected. The proton irradiation caused the increase of structural defects in HT-AlN buffer layer, which lead to the red shift of A_1 (LO) mode. The higher tails of XRD rocking curve indicated the introduction of point defects by irradiation. The full-width at half-maximum (FWHM) of E_2^high phonon mode broadened, which was consistent with change of FWHM of PL near-band-edge emission (BE). The spectra of yellow band normalized to the intensity of BE demonstrated a great increase of Ga vacancies related defects, which may be the main reason for the degradation of optical properties. [ABSTRACT FROM PUBLISHER]