The electron impact ionization rate and breakdown voltage inGaAs/Ga0.7Al0.3As MQW structures

The electron impact ionization rate (α) and breakdown voltage (V_BD) experimentally measured in a p⁺ -i-n⁺ diode structure with a GaAs/Ga_0.7Al _0.3As multiple quantum-well (MQW) i region are discussed. For structures with GaAs wells of 100 Å and barriers that vary from 7 to 60 Å in thickness, it is found that α is always less than α in bulk GaAs and that it decreases with increasing barrier thickness. The normalized V_BD also increases with increasing barrier thickness, confirming a decreasing ionization rate     

Al0.3Ga0.7As/GaAs HEMT's under opticalillumination

Theoretical and experimental work for the DC and RF performance of depletion mode Al_0.3Ga_0.7As/GaAs HEMTs under optical illumination is presented. The photoconductive effect increasing the 2-DEG channel electron concentration and photovoltaic effect in the gate junction are considered. Optical tuning of a 2 GHz HEMT oscillator and optical control of the gain of a 2 to 6 GHz HEMT amplifier are presented and potential applications are described     

120nm栅长In0.7Ga0.3As/In0.52Al0.48As HEMTs 器件

利用新型的PMMA/PMGI/ZEP520/PMGI四层胶T形栅电子束光刻技术制备出120nm栅长InP基雁配In0.7Ga0.3As/In0.52Al0.48As 高电子迁移率晶体管。制作出的InP基HEMT器件获得了良好的直流和高频性能,跨导、饱和漏电流密度、阈值电压、电流增益截止频率和最大单向功率增益频率分别达到520 mS/mm, 446 mA/mm, -1.0 V, 141 GHz 及 120 GHz。文中的材料结构和所有器件制备均为本研究小组自主研究开发。     

Buried-Pt gate InP/In0.52Al0.48As/In0.7Ga0.3As pseudomorphic HEMTs

InP-based high electron mobility transistors (HEMTs) were fabricated by depositing Pt-based multilayer metallization on top of a 6-nm-thick InP etch stop layer and then applying a post-annealing process. The performances of the fabricated 55-nm-gate HEMTs before and after the post-annealing were characterized and were compared to investigate the effect of the penetration of Pt through the very thin InP etch stop layer. After annealing at 250 °C for 5 min, the extrinsic transconductance (G_m) was increased from 1.05 to 1.17 S/mm and Schottky barrier height was increased from 0.63 to 0.66 eV. The unity current gain cutoff frequency (f_T) was increased from 351 to 408 GHz, and the maximum oscillation frequency (f_max) was increased from 225 to 260 GHz. These performance improvements can be attributed to penetration of the Pt through the 6-nm thick InP layer, and making contact on the InAlAs layer. The STEM image of the annealed device clearly shows that the Pt atoms contacted the InAlAs layer after penetrating through the InP layer.     

Enhanced device performance by unstrainedIn0.3Ga0.7As/In0.29Al0.71Asdoped-channel FET on GaAs substrates

An alternative In_0.3Ga_0.7As/In_0.29Al_0.71As heterostructure based on GaAs is proposed, which provides a large conduction-band discontinuity for a better carrier confinement, resulting in a high-carrier density. This unstrained high-In channel achieved a better device performance, as compared with the conventional pseudomorphic channel, which is always limited by the critical thickness. This unstrained channel is also proven to be more stable after a long-term biased-stress     

Logic Suitability of 50-nm In0.7 Ga0.3As HEMTs for Beyond-CMOS Applications

We have experimentally studied the suitability of nanometer-scale In_0.7Ga_0.3As high-electron mobility transistors (HEMTs) as an n-channel device for a future high-speed and low-power logic technology for beyond-CMOS applications. To this end, we have fabricated 50- to 150-nm gate-length In_0.7Ga_0.3As HEMTs with different gate stack designs. This has allowed us to investigate the role of Schottky barrier height (Phi_B) and insulator thickness (t_ins) on the logic characteristics of In_0.7Ga_0.3As HEMTs. The best 50-nm HEMTs with the highest Phi_B and the smallest t_ins exhibit an I_ON/I_OFF ratio in excess of 10⁴ and a subthreshold slope (S) below 86 mV/dec. These nonoptimized 50-nm In_0.7Ga_0.3As HEMTs also show a logic gate delay (CV/I) of around 1 ps at a supply voltage of 0.5 V, while maintaining an I_ON/I_OFF ratio above 10⁴, which is comparable to state-of-the-art Si MOSFETs. As one of the alternatives for beyond-CMOS technologies, we believe that InAs-rich InGaAs HEMTs hold a considerable promise.     

Ultrahigh-Speed 0.5 V Supply Voltage In0.7 Ga0.3As Quantum-Well Transistors on Silicon Substrate

The direct epitaxial growth of ultrahigh-mobility InGaAs/InAlAs quantum-well (QW) device layers onto silicon substrates using metamorphic buffer layers is demonstrated for the first time. In this letter, 80 nm physical gate length depletion-mode InGaAs QW transistors with saturated transconductance gm of 930 muS / mum and fT of 260 GHz at V_DS = 0.5 V are achieved on 3.2 mum thick buffers. We expect that compound semiconductor-based advanced QW transistors could become available in the future as very high-speed and ultralow-power device technology for heterogeneous integration with the mainstream silicon CMOS.     

Unstrained, modulation-doped, In0.3Ga0.7As/In0.29Al0.71As field-effect transistor grown on GaAssubstrate

The fabrication, structure, and properties of unstrained modulation-doped, 1-μm-long and 10-μm-wide gate, field effect transistors made of In_0.3Ga_0.7As/In_0.29As_0.71As heterojunctions grown on GaAs substrates using compositionally step-graded buffer layers are described. These devices have a transconductance of 335 mS/mm, f_max of 56 GHz, and a gate breakdown voltage of 23.5 V     

Dislocation scattering in n-type modulation dopedAl0.3Ga0.7As/InxGa1-xAs/Al0.3Ga0.7As quantum wells

The mobility due to misfit dislocation scattering in n-type modulation doped Al_0.3Ga_0.7As/In_xGa_1-xAs/Al _0.3Ga_0.7As quantum wells is discussed. Initially, the dislocations are modeled as an array of orthogonal charged lines. The scattering potential is introduced, including both the coulombic and piezoelectric components. The expression for the mobility limited by dislocation scattering is established, and the anisotropic characteristics of mobility and its variation with various material and device parameters are presented and discussed     

Transferring of GaAs microtips using selective wet etching Al0.7Ga0.3As sacrificial layer

GaAs pyramidal microtips were successfully transferred from GaAs substrate to target wafer by a simple technique, i.e., selective wet etching off AlGaAs sacrificial layer. A GaAs/Al_0.7Ga_0.3As/GaAs sandwich structure is firstly formed on GaAs (0 0 1) substrate by metalorganic chemical vapor deposition, and then GaAs pyramidal microtips are grown on the sandwich structure using selective liquid-phase epitaxy. The GaAs microtips are removed from the sandwich structure by selective wet etching Al_0.7Ga_0.3As layer using concentrated HCl solution. Finally, the tips are glued onto the target wafer by a negative photoresist. During this transfer process the tips are completely encapsulated in a positive photoresist to protect against attack. Scanning electron microscopy images show that GaAs tips can be successfully transferred without any damage by this technique. The achievement reported here represents a significant step towards the application of scanning near-field optical microscopy.     

Thermal stability of MISFET with low-temp molecular-beamepitaxy-grown GaAs and Al0.3Ga0.7As gate ins

GaAs and Al_0.3Ga_0.7As epilayers grown at LT by MBE were used as insulators in the fabrication of MISFET devices. Parametric changes were used to evaluate the thermal stability of MISFET, to identify failure mechanisms and validate the reliability of these devices. The LT-Al_0.3Ga_0.7As MISFET showed superior thermal stability. The degradation in the performance of MISFET with 1000 Å thick LT-GaAs gate insulator was worse than those of the MESFET. On the other hand, MISFET with 250 Å thick LT-GaAs gate insulators exhibited stable characteristics with thermal stressing, LF (low frequency) noise studies on the TLM structures of MISFET layers exhibited 1/f noise in the LT-Al_0.3Ga_0.7As samples and 250 Å LT-GaAs samples; whereas the 1000 Å thick LT-GaAs samples exhibited 1/f^3/2 noise, which was attributed to: (i) the thermal noise generated at the interface of the insulator, and (ii) the active layer due to the outdiffused metallic arsenic. Reverse gate-drain current degradation experiments were carried out at 120°C, 160°C, 200°C, and 240°C. Transconductance frequency dispersion studies were carried out before and after thermal stress on these MISFET. The transconductance of MISFET with 1000 Å LT-GaAs gate insulators was degraded by 40% at 100 kHz after thermal stress. The rest of the samples exhibited stable characteristics. These results indicate that composition changes had occurred at the interface in thicker LT-GaAs MISFET structures. Thinner LT-layers are ideal for achieving higher transconductance and better thermal stability without sacrificing the power capability of MISFET     

GaAs/Al0.3Ga0.7As QWIP 暗电流特性HRTEM 研究

采用金属有机物化学气相沉积法(MOCVD)生长GaAs/Al0.3Ga0.7As 量子阱材料,制备300 m300 m 台面,内电极压焊点面积为20 m20 m,外电极压焊点面积为80 m80 m 的单元样品两种。用变温液氮制冷系统对样品进行77 ~300 K 暗电流特性测试。结果显示,器件暗电流曲线呈现出正负偏压的不对称性。利用高分辨透射扫描电镜(HRTEM)获得样品纳米尺度横断面高分辨像,分析结果表明:样品横断面处存在不同程度的位错及不均匀性。说明样品内部穿透位错造成相位分离是引起量子阱光电性能变差的根本原因,不同生长次序中AlGaAs 与GaAs 界面的不对称性与掺杂元素的扩散现象加剧了暗电流曲线的不对称性。     

Spectral characteristics ofsingle-In0.7Ga0.3As quantum-well microring lasers

Low-threshold optically pumped microring and disk lasers containing a single compressive strained In0.7Ga_0.3As quantum well are characterized. Strong bandfilling in single quantum wells is used to show saturation of the background spontaneous emission in microrings compared with comparable microdisks. The continuous wave threshold pump power for a microring is as low as 2 μW (3 W/cm² ) at liquid nitrogen temperatures. The lasers operate multimoded with wavelengths determined by whispering gallery modes of several orders     

Metamorphic In0.4Al0.6As/In0.4Ga0.6As HEMTs on GaAs substrate

New In_0.4Al_0.6As/In_0.4Ga_0.6 As metamorphic (MM) high electron mobility transistors (HEMTs) have been successfully fabricated on GaAs substrate with T-shaped gate lengths varying from 0.1 to 0.25 μm. The Schottky characteristics are a forward turn-on voltage of 0.7 V and a gate breakdown voltage of -10.5 V. These new MM-HEMTs exhibit typical drain currents of 600 mA/mm and extrinsic transconductance superior to 720 mS/mm. An extrinsic current cutoff frequency f_T of 195 GHz is achieved with the 0.1-μm gate length device. These results are the first reported for In_0.4 Al_0.6As/In_0.4Ga_0.6As MM-HEMTs on GaAs substrate     

GaAs/Al0.3Ga0.7As resonant tunneling diodes with atomically flat interfaces grown on (411)A GaAs substrates by MBE

Al_0.3Ga_0.7As (10 nm)/GaAs (5 nm)/Al_0.3Ga_0.7As (10 nm) double barrier resonant tunneling diodes (RTDs) have been fabricated on a (411)A GaAs substrate by molecular beam epitaxy (MBE), which has atomically flat GaAs/Al_0.3Ga_0.7As interfaces over a device area. The (411)A RTDs showed a larger peak to valley current ratio by about 40% at 77K comparing to RTDs grown on a conventional (100) GaAs substrate simultaneously. Reduction of the valley current (0.61 times smaller) is the main cause for this larger peak to valley current ratio, which is probably due to improved interface roughness and defects of the (411)A RTDs.     

Fabrication of 80-nm T-gate high indium In0.7Ga0.3As/In0.6Ga0.4As composite channels mHEMT on GaAs substrate with simple technological process

An 80-nm gate length metamorphic high electron mobility transistor (mHEMT) on a GaAs substrate with high indium composite compound-channels In_0.7Ga_0.3As/In_0.6Ga_0.4As and an optimized grade buffer scheme is presented. High 2-DEG Hall mobility values of 10200 cm²/(V· s) and a sheet density of 3.5 × 10¹² cm^-2 at 300 K have been achieved. The device's T-shaped gate was made by utilizing a simple three layers electron beam resist, instead of employing a passivation layer for the T-share gate, which is beneficial to decreasing parasitic capacitance and parasitic resistance of the gate and simplifying the device manufacturing process. The ohmic contact resistance R_c is 0.2 Ω ·mm when using the same metal system with the gate (Pt/Ti/Pt/Au), which reduces the manufacturing cycle of the device. The mHEMT device demonstrates excellent DC and RF characteristics. The peak extrinsic transconductance of 1.1 S/mm and the maximum drain current density of 0.86 A/mm are obtained. The unity current gain cut-off frequency (f_T) and the maximum oscillation frequency (f_max) are 246 and 301 GHz, respectively.     

Band offsets of In0.30Ga0.70As/In0.29Al0.71As heterojunction grown on GaAs substrate

Temperature-dependent current-voltage measurement was employed to study the band offsets of the In_0.30Ga_0.70As/In _0.29Al_0.71As heterojunction. The conduction band discontinuity was determined to be 0.71±0.05 eV which corresponds to a conduction band offset to bandgap difference ratio ~0.66. The comparison between experimental and theoretical results is presented     

GaAs-Al_(0.3)Ga_(0.7)As DH共腔双二极管激光器

本文报导了GaAs-Al_(0.3)Ga_(0.7)AsDH共腔双二极管激光器的实验制备。对这种激光器的稳态输出特性和瞬态输出特性作了实验观测。     

A new Al0.3Ga0.7As/GaAs modulation-doped FET

A new Al0.3Ga0.7As/GaAs modulation-doped FET fabricated like a MESFET but operating like a JFET was successfully fabricated and tested. This new device replaces the Schottky gate of the MESFET with an n+/p+ camel diode structure, thereby allowing problems associated with the former to be overcome. The devices, which were fabricated from structures grown by molecular beam epitaxy (MBE), had a 1µm gate length, a 290µm gate width, and a 4µm channel length. The room temperature transconductance normalized to the gate width was about 95 mS/mm, which is comparable to that obtained in similar modulation-doped Schottky barrier FET's. Unlike modulation-doped Schottky barrier FET's, fabrication of this new device does not require any critical etching steps or formation of a rectifying metal contact to the rapidly oxidizing Al0.3Ga0.7As. Relatively simple fabrication procedures combined with good device performance make this camel gate FET suitable for LSI applications.