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     

High-performance In0.08Ga0.92As MESFETs onGaAs(100) substrates

In_0.08Ga_0.92As MESFETs were grown in GaAs (100) substrates by molecular beam epitaxy (MBE). The structure comprised an undoped compositionally graded In_xGa_1-x As buffer layer, an In_0.08Ga_0.92As active layer, and an n⁺-In_0.08Ga_0.92As cap layer. FETs with 50-μm width and 0.4-μm gate length were fabricated using the standard processing technique. The best device showed a maximum current density of 700 mA/mm and a transconductance of 400 mS/mm. The transconductance is extremely high for the doping level used and is comparable to that of a 0.25-μm gate GaAs MESFET with an active layer doped to 10¹⁸ cm^-3. The current-gain cutoff frequency was 36 GHz and the power-gain cutoff frequency was 65 GHz. The current gain cutoff frequency is comparable to that of a 0.25-μm gate GaAs MESFET     

In0.52Al0.48As/InAs/InxAl1-xAs pseudomorphic HEMT's on InP

The DC and microwave performance of an InAs channel HEMT is reported. Room-temperature electron mobility as high as 20200 cm² /Vs is measured, with a high carrier concentration of 2.7×10 ¹² cm^-2. DC extrinsic transconductance of 714 mS/mm is measured and a unity-current-gain cut-off frequency of 50 GHz is obtained for a 1.1-μm gate length HEMT. The success of achieving superior Hall mobility and device performance is strongly dependent on the In_xAl_1-xAs buffer layer design that changes the lattice constant from lattice-matched In_0.52Al_0.48 As to In_0.75Al_0.25As. The multiple In_0.52Al_0.48As/InAs monolayer superlattices buffer achieves the best performance as compared to the step-graded In_x Al_1-xAs and the uniform In_0.76Al_0.25 As buffer     

Electron transport in 0.15-μm gate In0.52Al0.48As/In0.53Ga0.47As HEMT

Magneto-transport and cyclotron resonance measurements were made to determine directly the density, mobility, and the effective mass of the charge carriers in a high-performance 0.15-μm gate In_0.52 Al_0.48As/In_0.53Ga_0.47As high-electron-mobility transistor (HEMT) at low temperatures. At the gate voltage V_G=0 V, the carrier density n _g under the gate is 9×10¹¹ cm^-2, while outside of the gate region n_g=2.1×10¹² cm^-2. The mobility under the gate at 4.2 K is as low as 400 cm²/V-s when V_G<0.1 V and rapidly approaches 11000 cm²/V-s when V_G>0.1 V. The existence of this high mobility threshold is crucial to the operation of the device and sets its high-performance region in V_G>0.1 V     

Characteristics of strained In0.65Ga0.35As/In0.52Al0.48As HEMT withoptimized transport parameters

The DC and microwave performance of a strained In₀.₆₅Ga₀.₃₅As/In₀ .₅₂A1₀.₄₈As HEMT (high-electron-mobility transistors) is reported. Its design is based on theoretical and experimental studies including low- and high-field transport characterization of heterostructures with different strains. The intrinsic DC transconductance and cutoff frequence of 1.4-μm-long gate HEMTs are 574 mS/mm and 38.6 GHz, respectively. The increased indium (In) composition in the channel enhances the drift velocity from 1.35×10⁷ to 1.55×10⁷ cm/s at 300 K     

In0.52Al0.48As/In0.53Ga0.47As double-heterojunction p-n-p bipolar transistors grown bymolecular beam epitaxy

P-n-p In_0.52Al_0.48As/In_0.53Ga_0.47 As double-heterojunction bipolar transistors with a p⁺-InAs emitter cap layer grown by molecular-beam epitaxy have been realized and tested. A five-period 15-Å-thick In_0.53Ga_0.47As/InAs superlattice was incorporated between the In_0.53Ga_0.47As and InAs cap layer to smooth out the valence-band discontinuity. Specific contact resistance of 1×10^-5 and 2×10^-6 Ω-cm² were measured for nonalloyed emitter and base contacts, respectively. A maximum common emitter current gain of 70 has been measured for a 1500-Å-thick base transistor at a collector current density of 1.2×10³ A/cm². Typical current gains of devices with 50×50-μm² emitter areas were around 50 with ideality factors of 1.4     

Characterization of surface-undoped In0.52Al0.48As/In0.53Ga0.47As/InP high electron mobilitytransistors

High-performance 0.3-μm-gate-length surface-undoped In_0.52 Al_0.48As/In_0.53Ga_0.47As/InP high-electron-mobility transistors (HEMTs) grown by molecular beam epitaxy (MBE) have been characterized and compared with a surface-doped structure. At 18 GHz, the surface-undoped HEMT has achieved a maximum stable gain (MSG) of 19.2 dB compared to 16.0 dB for the surface-doped structure. The higher MSG value of the surface-undoped HEMTs is obtained due to the improved g_m/g₀ ratio associated with the surface-induced electric field spreading effect. Comparison of identical 0.3-×150-μm-gate devices fabricated on surface-undoped and -doped structures has shown greatly improved gate leakage characteristics and much lower output conductance for the surface-undoped structure. It is demonstrated that the surface potential, modulated by different surface layer designs, affects the charge control in the conducting channel, especially the carrier injection into the buffer, resulting in excess output conductance. Several millimeter-wave coplanar waveguide (CPW) monolithic distributed amplifiers have been successfully fabricated by using the surface-undoped HEMT structure. A high gain per stage distributed amplifier with 170-dB±1-dB small-signal gain across a frequency band of 24-40 GHz, a W-band monolithic integrated circuit with 6.4-dB gain at 94 GHz, and a broad bandwidth distributed amplifier with 5-dB gain across a frequency band of 5 to 100 GHz have been demonstrated by using the surface-undoped structures     

Improved strained HEMT characteristics using double-heterojunctionIn0.65Ga0.35As/In0.52Al0.48As design

The DC and microwave properties of strained In_0.65Ga _0.35As/In₀₅₂Al_0.48As HEMTs (high electron-mobility transistors) with double-heterojunction design are presented. The high sheet carrier density and good carrier confinement give rise to excellent device performance with very low output conductance. For 1×150-μm² long-gate HEMTs, the measured cutoff frequency f_T and maximum frequency of oscillation f_max are as high as 37 and 66 GHz, respectively     

0.12 μm transferred-substrateIn0.52Al0.48As/In0.53Ga0.47As HEMTs on silicon wafer

New In_0.52Al_0.48As/In_0.53Ga_0.47 As transferred-substrate high electron mobility transistors (TS-HEMTs) have been successfully fabricated on 2-in Silicon substrate with 0.12 μm T-shaped gate length. These new TS-HEMTs exhibit typical drain currents of 450 mA/mm and extrinsic transconductance up to 770 mS/mm. An extrinsic current gain cutoff frequency f_T of 185 GHz is obtained. That result is the first reported for In_0.52Al_0.48As/In_0.53Ga_0.47 As TS-HEMTs on Silicon substrate     

Ga0.51In0.49P/In0.15Ga0.85As/GaAs pseudomorphic doped-channel FET with high-current densityand high-breakdown voltage

Ga_0.51In_0.49P/In_0.15Ga_0.85 As/GaAs pseudomorphic doped-channel FETs exhibiting excellent DC and microwave characteristics were successfully fabricated. A high peak transconductance of 350 mS/mm, a high gate-drain breakdown voltage of 31 V and a high maximum current density (575 mA/mm) were achieved. These results demonstrate that high transconductance and high breakdown voltage could be attained by using In_0.15Ga_0.85As and Ga_0.51In_0.49P as the channel and insulator materials, respectively. We also measured a high-current gain cut-off frequency f_t of 23.3 GHz and a high maximum oscillation frequency f_max of 50.8 GHz for a 1-μm gate length device at 300 K. RF values where higher than those of other works of InGaAs channel pseudomorphic doped-channel FETs (DCFETs), high electron mobility transistors (HEMTs), and heterostructure FETs (HFETs) with the same gate length and were mainly attributed to higher transconductance due to higher mobility, while the DC values were comparable with the other works. The above results suggested that Ga_0.51In_0.49P/In_0.15Ga_0.85 As/GaAs doped channel FET's were were very suitable for microwave high power device application     

In0.52Al0.48As/In0.53Ga0.47As MSM photodetectors and HEMT's grown by MOCVD on GaAs substrates

The authors report the first demonstration of In_0.52Al _0.48As/In_0.53Ga_0.47As metal-semiconductor-metal (MSM) photodetectors and high-electron-mobility transistors (HEMTs) grown on GaAs substrates by organometallic chemical vapor deposition. Both photodetectors and transistors showed no degradation in performance compared to devices simultaneously grown on InP substrates. The photodetectors exhibited a responsivity of 0.45 A/W and leakage current of 10 to 50 nA. The HEMTs with a gate length of 1.0 μm showed a transconductance as high as 250 mS/mm, and f_T and f_max of 25 and 70 GHz, respectively     

Fabrication of 0.15-μm Γ-Shaped Gate In0.52Al0.48As/In0.6Ga0.4As Metamorphic HEMTs Using DUV Lithography and Tilt Dry-Etching Technique

An In_0.52Al_0.48As/In_0.6Ga_0.4 As metamorphic high-electron mobility transistor (MHEMT) with 0.15-mum Gamma-shaped gate using deep ultraviolet lithography and tilt dry-etching technique is demonstrated. The developed submicrometer gate technology is simple and of low cost as compared to the conventional E-beam lithography or other hybrid techniques. The gate length is controllable by adjusting the tilt angle during the dry-etching process. The fabricated 0.15-mum In_0.52Al_0.48As/In_0.6Ga_0.4As MHEMT using this novel technique shows a saturated drain-source current of 680 mA/mm and a transconductance of 728 mS/mm. The f_T and f_max of the MHEMT are 130 and 180 GHz, respectively. The developed technique is a promising low-cost alternative to the conventional submicrometer E-beam gate technology used for the fabrication for GaAs MHEMTs and monolithic microwave integrated circuits     

In0.53Ga0.47As MSM photodiodes withtransparent CTO Schottky contacts and digital superlattice grading

Metal-semiconductor-metal (MSM) photodiodes with an In_0.53 Ga_0.47As active region were investigated using a transparent cadmium tin oxide (CTO) layer for the interdigitated electrodes to improve the low responsivity of conventional MSM photodiodes with opaque electrodes. CTO is suitable as a Schottky contact, an optical window and an anti-reflection (AR) coating. The transparent contact prevents shadowing of the active layer by the top electrode, thus allowing greater collection of incident light. Responsivity of CTO-based MSM photodiodes with 1-μm finger widths and 2-μm finger spacings and without an AR coating between the electrodes was twice (0.62 A/W) that of a similar MSM photodiodes with Ti/Au electrodes (0.30 A/W). A thin 800 Å In_0.52Al_0.48 As layer was inserted below the electrodes to elevate the electrode Schottky barrier height. A digitally graded superlattice region (660 A) was also employed to reduce carrier trapping at the In _0.53Ga_0.47As/In_0.52Al_0.48As heterointerface which acts to degrade photodiode bandwidth. Bandwidth of opaque electrode MSMs was elevated nearly an order of magnitude over a previous MSM photodiode design with an abrupt heterointerface, whereas the bandwidth of transparent electrode MSM's only improved about five times, indicating resistive effects may be intervening     

An In0.52Al0.48As/n+-In0.53Ga0.47As MISFET with a modulation-doped channel

A heterostructure metal-insulator-semiconductor field-effect transistor (MISFET) with a modulation-doped channel is proposed. In this device, a very thin undoped subchannel is located between the undoped wide-bandgap insulator and a thin heavily doped channel. In the depletion mode of operation, electron transport takes place along the heavily doped channel. When the device enters the accumulation mode of operation, electrons pile up against the heterointerface in the high-mobility undoped subchannel. This results in markedly improved transport characteristics at the onset of accumulation. The concept is demonstrated in the In_0.52Al_0.48As/In_0.53 Ga_0.47As system on InP. A 1.5-μm-gate-length MISFET shows a unity current-gain cutoff frequency of 37 GHz     

Gate-length dependence of DC and microwave properties ofsubmicrometer In0.53Ga0.47As HIGFETs

In_0.52Al_0.48As/In_0.53Ga_0.47 As/InP heterostructure insulated-gate field-effect transistors (HIGFETs) with gate lengths from 1.1 and 0.3 μm have been fabricated, and their electrical performance is characterized at DC and microwave frequencies. The refractory-gate self-aligned process, applied to devices with In_0.53Ga_0.47As channels, yields an unprecedented combination of very-high speed and excellent uniformity. HIGFETs with L_g=0.6 μm showed average peak transconductance g_m of 528 mS/mm and unity-current-gain cutoff frequency f_t of 50 GHz. The uniformity of g_m was better than 1%, and the voltage of the g_m peak was uniform to ±30 mV. HIGFETs with L_g=0.3 μm showed f₁ up to 63 GHz, but suffered from serious short-channel effect, due to excessive thickness of the InGaAs channel layer. A self-aligned technique for gate resistance reduction is shown to substantially improve microwave power gain     

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.     

Optical control and injection locking of monolithically integratedIn0.53Ga0.47As/In0.52Al0.48As MODFET oscillators

Optical tuning and injection locking characteristics of MMIC oscillators made with InP-based 0.25 μm gate In_0.53Ga_0.47As/In_0.52Al_0.48 As modulation-doped field-effect transistors (MODFETs) have been investigated. Optical tuning has been performed on the X- and R-band oscillator circuits and a maximum tuning range of 8.7 MHz and 11.7 MHz, respectively, has been measured. The tuning characteristics have been explained in terms of changes in the MODFET characteristics with absorption of incident light. Direct optical subharmonic injection locking of these oscillator circuits have been done at 10 and 19 GHz, which are the highest achieved for InP-based MMIC's     

0.2-μm gate-length atomic-planar doped pseudomorphic Al0.3Ga0.7As/In0.25Ga0.75As MODFETswith fT over 120 GHz

The authors report the DC and RF performance of nominally 0.2-μm-gate length atomic-planar doped pseudomorphic Al_0.3Ga_0.7As/In_0.25Ga_0.75As modulation-doped field-effect transistors (MODFETs) with f_T over 120 GHz. The devices exhibit a maximum two-dimensional electron gas (2 DEG) sheet density of 2.4×10¹² cm^-2, peak transconductance g _m of 530-570 mS/mm. maximum current density of 500-550 mA/mm, and peak current-gain cutoff frequency f_T of 110-122 GHz. These results are claimed to be among the best ever reported for pseudomorphic AlGaAs/InGaAs MODFETs and are attributed to the high 2 DEG sheet density, rather than an enhanced saturation velocity, in the In_0.25Ga_0.75As channel     

Impact of surface layer on In0.52Al0.48As/In0.53Ga0.47As/InP high electron mobilitytransistors

The surface potential of FETs has shown a strong effect on the channel potential and charge control in the channel. A study of the role of undoped versus doped cap layers in In_0.52Al_0.48As-In_0.53Ga_0.47 As-InP high-electron-mobility transistors (HEMT) is discussed. As the result of surface potential effect, direct comparison of 0.3×150-μm² gate devices yielded improved gate breakdown characteristics and a DC output conductance of less than 15 mS/mm for the surface undoped structure compared to 50 mS/mm for the doped structure. The surface undoped MEMT achieved a very high maximum stable gain of 19.2 dB compared to 16.0 dB for the surface doped HEMT at 18 GHz, largely due to the improved g_m/g ₀ ratio. This study demonstrates that control of the surface potential in In_0.52Al_0.48As-In_0.53Ga _0.47As-InP HEMTs is consistent with the effect of a gate recess in MESFETs. This study also shows that, in achieving high-gain applications of HEMTs, the surface potential near the gate edge should be optimized through unconventional surface layer design     

Highly lattice-mismatched In0.26Ga0.74As/GaAsMESFET's: impact of critical thickness on device performance

Fabrication of 0.25-μm-gate MESFETs directly on In_0.26 Ga_0.74As epitaxial layers which are much thicker than the pseudomorphic critical thickness is described. The InAs mole fraction is increased in the MESFET channel to 26%. Whether the device performance can be further improved without detrimental dislocation effects as the channel thickness exceeds the critical thickness considerably is investigated. Despite large lattice mismatch and high defect density, these devices show excellent microwave performance with an extrinsic f_t of 120 GHz. Bias-dependent S-parameters indicate that the In_0.26Ga_0.74As MESFET maintains excellent device performance down to very low drain current without showing any performance degradation due to misfit or threading dislocations