An improved ASM-HEMT model for kink effect on GaN devices

With the analysis of experiment and theory on GaN HEMT devices under DC sweep,an improved model for kink effect based on advanced SPICE model for high electron mobility transistors(ASM-HEMT)is pro⁃posed,considering the relationship between the drain/gate-source voltage and kink effect.The improved model can not only accurately describe the trend of the drain-source current with the current collapse and kink effect,but also precisely fit different values of drain-source voltages at which the kink effect occurs under different gatesource voltages.Furthermore,it well characterizes the DC characteristics of GaN devices in the full operating range,with the fitting error less than 3%.To further verify the accuracy and convergence of the improved model,a load-pull system is built in ADS.The simulated result shows that although both the original ASM-HEMT and the improved model predict the output power for the maximum power matching of GaN devices well,the im⁃proved model predicts the power-added efficiency for the maximum efficiency matching more accurately,with 4%improved.

结构参数对N极性面GaN/InAlN高电子迁移率晶体管性能的影响

基于漂移-扩散传输模型、费米狄拉克统计模型以及Shockley-Read-Hall复合模型等,通过自洽求解薛定谔方程、泊松方程以及载流子连续性方程,模拟研究了材料结构参数对N极性面GaN/InAlN高电子迁移率晶体管性能的影响及其物理机制.结果表明,增加GaN沟道层的厚度(5-15 nm)与InAlN背势垒层的厚度(10-40 nm),均使得器件的饱和输出电流增大,阈值电压发生负向漂移.器件的跨导峰值随Ga N沟道层厚度的增加与InAlN背势垒层厚度的减小而减小.模拟中,各种性能参数的变化趋势均随GaN沟道层与InAlN背势垒层厚度的增加而逐渐变缓,当GaN沟道层厚度超过15 nm、InAlN背势垒层厚度超过40 nm后,器件的饱和输出电流、阈值电压等参数基本趋于稳定.材料结构参数对器件性能影响的主要原因可归于器件内部极化效应、能带结构以及沟道中二维电子气的变化.

Vacuum Violet Photo-Response of AlGaN-Based Metal-Semiconductor-Metal Photodetectors

Al_(0.5)Ga_(0.5)N-based metal-semiconductor-metal photodetectors(PDs)with a large device area of 5×5 mm^(2) are fabricated on a sapphire substrate,which are tested for vacuum ultraviolet light detection by using a synchrotron radiation source.The PD exhibits low dark current of less than 1 pA under 30 V bias and a spectral cutoff around 260 nm,corresponding to the energy bandgap of Al_(0.5)Ga_(0.5)N.A peak photo-responsivity of 14.68 mA/W at 250 nm with a rejection ratio(250/360 nm)of more than four orders of magnitude is obtained under 30 V bias.For wavelength less than 170 nm,the photoresponsivity of the PD is found to increase as wavelength decreases,which is likely caused by the enhanced photoemission effect.

High Deep-Ultraviolet Quantum Efficiency GaN P–I–N Photodetectors with Thin P-GaN Contact Layer

GaN ultraviolet(UV)p-i-n photodetectors(PDs)with a 40 nm thin p-GaN contact layer are fabricated on sapphire substrates,which exhibit enhanced quantum efficiency especially in a deep-UV wavelength range.The PDs show good rectification behavior and low dark current in pA level for reverse bias up to-10 V.Under zero bias,the maximum quantum efficiency of the PD at 360 nm is close to 59.4%with a UV/visible rejection ratio more than 4 orders of magnitude.Even at a short wavelength of 280 nm,the quantum efficiency of the PD is still around 47.5%,which is considerably higher than that of a control device with a thicker p-GaN contact layer.The room temperature thermal noise limited detectivity of the PD is calculated to be~4.96×10^(14) cm·Hz^(1/2)W^(-1).

High Quantum Efficiency Back-Illuminated AlGaN-Based Solar-Blind Ultraviolet p-i-n Photodetectors

AlGaN-based back-illuminated solar-blind ultraviolet(UV)p–i–n photodetectors(PDs)with high quantum efficiency are fabricated on sapphire substrates.To improve the overall performance of the PD,a series of structural design considerations and growth procedures are implemented in the epitaxy process.A distinct wavelength-selective photo-response peak of the PD is obtained in the solar-blind region.When operating in photovoltaic mode,the PD exhibits a solar-blind/UV rejection ratio of up to 4 orders of magnitude and a peak responsivity of~113.5 mA/W at 270 nm,which corresponds to an external quantum efficiency of~52%.Under a reverse bias of-5 V,the PD shows a low dark current of~1.8 pA and an enhanced peak quantum efficiency of~64%.The thermal noise limited detectivity is estimated to be~3.3×10^(13) cm·Hz^(1/2)W^(-1).

GaN Schottky Barrier Diodes with High-Resistivity Edge Termination Formed by Boron Implantation

Edge termination is one of the key technologies for fabricating high voltage Schottky barrier diodes(SBDs),which could effectively reduce the peak electric field along the Schottky contact edge and enhance the breakdown voltage.We adopt a high-resistivity ring structure as the edge termination for planar GaN SBDs.The edge termination is formed by self-aligned boron implantation on the edge of devices to form a highly damaged layer.In the implant dose and energy ranges studied experimentally,the GaN SBDs show improved blocking characteristics in terms of reverse leakage current and breakdown voltage at higher implant dose or implant energy.Meanwhile,the forward turn-on characteristics of the GaN SBDs exhibit no apparent change.

The Effects of Polarization on the Current Transport Mechanisms for UV-LEDs

The effects of a polarization field on the current transport mechanisms in ultraviolet light emitting diodes(UV-LEDs)are studied by analyzing forward current-voltage(I–V)characteristics based on the experimental data and theoretical simulation.The results indicate that polarization electric field suppresses the diffusion current and meanwhile enhances the tunneling current in the metal-face UV LEDs under forward bias.The presence of a large polarization field in the deep UV-LEDs is responsible for the current transport mechanism dominated by the tunneling process at a moderate forward bias.

Improved Programming Efficiency through Additional Boron Implantation at the Active Area Edge in 90 nm Localized Charge-Trapping Non-volatile Memory

As the scaling-down of non-volatile memory （NVM） cells continues, the impact of shallow trench isolation （STI） on NVM cells becomes more severe. It has been observed in the 90nm localized charge-trapping non-volatile memory （NROMTM） that the programming efficiency of edge cells adjacent to STI is remarkably lower than that of other cells when channel hot electron injection is applied. Boron segregation is found to be mainly responsible for the low programming efficiency of edge cells. Meanwhile, an additional boron implantation of 10°tilt at the active area edge as a new solution to solve this problem is developed.

A 1100＋ V A1GaN/GaN-Based Planar Schottky Barrier Diode without Edge Termination

AlGaN/GaN-based planar Schottky barrier diodes with various spacings between ohmic and Schottky contacts are fabricated without any edge termination. The reverse leakage current of the devices quickly saturates at low reverse bias when the two-dimensional electron gas （2DEG） at the AIGaN/GaN interface is fully depleted. The corresponding breakdown voltage is found to follow a linear dependence on contact spacing and exceeds 1100 V at a contact spacing of 20Jim, yielding a high V2BR/Rox value of 〉 280 MW.em-2. The observations are tentatively explained by a ＂natural super-junetion＂ theory, in whieh ionized surface stgtes at front surface of the AIGaN barrler have to be neutralized by revenqe surface leakage current from the Sehottky electrode.