AlSb/InAs HEMT's for low-voltage, high-speed applications

The design, fabrication, and characterization of 0.1 μm AlSb/InAs HEMT's are reported. These devices have an In_0.4Al _0.6As/AlSb composite barrier above the InAs channel and a p ⁺ GaSb layer within the AlSb buffer layer. The HEMT's exhibit a transconductance of 600 mS/mm and an f_T of 120 GHz at V_Ds=0.6 V. An intrinsic f_T of 160 GHz is obtained after the gate bonding pad capacitance is removed from an equivalent circuit. The present HEMT's have a noise figure of 1 dB with 14 dB associated gain at 4 GHz and V_Ds=0.4 V. Noise equivalent circuit simulation indicates that this noise figure is primarily limited by gate leakage current and that a noise figure of 0.3 dB at 4 GHz is achievable with expected technological improvements. HEMT's with a 0.5 μm gate length on the same wafer exhibit a transconductance of 1 S/mm and an intrinsic f_TL_g, product of 50 GHz-μm     

Room-temperature InAs=AlSb quantum-cascade laser operating at 8.9 /spl mu/m

A room-temperature InAs/AlSb quantum-cascade laser operating at 8.9 mum is reported. The laser structure is grown on an n-InAs (100) substrate by solid-source molecular-beam epitaxy. The active region utilises a diagonal intersubband transition in an InAs/AlSb three-quantum-well structure. Observed threshold current density in pulse mode is 2.6 kA/cm² at 80 K and 12.0 kA/cm² at 300 K. The maximum operation temperature is 305 K     

InAs/AlSb double-barrier structure with large peak-to-valleycurrent ratio: a candidate for high-frequency microwave devices

Negative differential resistance (NDR) in InAs/AlSb/InAs/AlSb/InAs double-barrier structures with peak-to-valley current (PVC) ratios as large as 11 at room temperature and 28 at 77 K is reported. This is a large improvement over previous results for these materials and is also considerably better than those obtained for the extensively studied GaAs/AlGaAs material system. The peak current density was also improved by reducing the barrier thickness, and values exceeding 10⁵ A/cm² have been observed. These results suggest that InAs/AlSb structures are interesting alternatives to conventional GaAs/AlGaAs structures in high-frequency devices. NDR in a InAs/AlSb superlattice double-barrier structure with a lower PVC ratio than in the solid barrier case has also been observed. This result indicates that valley current contributions arising from X-point tunneling are negligible in these structures, consistent with the large band offset     

1.7-ps, microwave, integrated-circuit-compatible InAs/AlSb resonanttunneling diodes

Microwave integrated-circuit-compatible InAs/AlSb resonant tunneling diodes (RTDs) have been fabricated. The resulting devices have peak current densities of 3.3×10⁵ A/cm² with peak-to-valley ratios of 3.3. Switching transition times of 1.7 ps are measured using electrooptic sampling techniques     

High-transconductance delta-doped InAs/AlSb HFETs with ultrathinsilicon-doped InAs quantum well donor layer

Modulation-doping of InAs/AlSb quantum wells generally requires the use of chalcogenide donor impurities because silicon, the usual donor of choice in MBE, displays an amphoteric behavior in antimonide compounds. In this letter, we demonstrate the use of an ultrathin 9 Å silicon doped InAs well to delta-dope the current-carrying InAs channel of an InAs/AlSb heterostructure field-effect transistor (HFET). Using this new approach, we have fabricated delta-doped 0.6-μm gate InAs/AlSb HFETs with a measured extrinsic transconductance of 800 mS/mm at V_DS=0.8 V, a cutoff frequency f_T=60 GHz (F_MAX=87 GHz), and well-behaved I-V curves. HFET's with a 2-μm gatelength also feature very high transconductances in the 700-800 mS/mm range at V_DS=1.5 V. The present work eliminates the requirement for chalcogenide compound donor sources to delta-dope InAs/AlSb quantum wells by allowing the use of silicon in the fabrication of high-performance InAs/AlSb HFET's     

High-performance, 0.1 μm InAlAs/InGaAs high electron mobilitytransistors on GaAs

This letter describes the material characterization and device test of InAlAs/InGaAs high electron mobility transistors (HEMTs) grown on GaAs substrates with indium compositions and performance comparable to InP-based devices. This technology demonstrates the potential for lowered production cost of very high performance devices. The transistors were fabricated from material with room temperature channel electron mobilities and carrier concentrations of μ=10000 cm² /Vs, n=3.2×10¹² cm^-2 (In=53%) and μ=11800 cm²/Vs, n=2.8×10¹² cm^-2 (In=60%). A series of In=53%, 0.1×100 μm² and 0.1×50 μm² devices demonstrated extrinsic transconductance values greater than 1 S/mm with the best device reaching 1.074 S/mm. High-frequency testing of 0.1×50 μm² discrete HEMT's up to 40 GHz and fitting of a small signal equivalent circuit yielded an intrinsic transconductance (g_m,i) of 1.67 S/mm, with unity current gain frequency (f_T) of 150 GHz and a maximum frequency of oscillation (f_max) of 330 GHz. Transistors with In=60% exhibited an extrinsic g_m of 1.7 S/mm, which is the highest reported value for a GaAs based device     

Gate-Recess Technology for InAs/AlSb HEMTs

The gate-recess technology for Si $delta$-doped InAs/AlSb high-electron-mobility transistors (HEMTs) has been investigated by combining atomic force microscopy (AFM) inspection of the gate-recess versus time with electrical device characterization. Deposition of the gate metal on the $hbox{In}_{0.5}hbox{Al}_{0.5}hbox{As}$ protection layer or on the underlying AlSb Schottky layer resulted in devices suffering from high gate-leakage current. Superior dc and high frequency device performance were obtained for HEMTs with an insulating layer between the gate and the Schottky layer resulting in a reduction of the gate leakage current $I_{G}$ by more than two orders of magnitude at a drain-to-source voltage $V_{DS}$ of 0.1 V. The existence of this intermediate insulating layer was evident from the electrical measurements. AFM measurements suggested that the insulating layer was due to a native oxidation of the AlSb Schottky layer. The insulated-gate HEMT with a gate length of 225 nm exhibited a maximum drain current $I_{D}$ higher than 500 mA/mm with good pinchoff characteristics, a dc transconductance $g_{m}$ of 1300 mS/mm, and extrinsic values for cutoff frequency $f_{T}$ and maximum frequency of oscillation $f_{max}$ of 160 and 120 GHz, respectively.      

Low-temperature characteristics of 0.35 μm AlSb/InAs HEMTs

The effects of low temperature on the characteristics of 0.35 μm gate-length AlSb/InAs HEMTS are reported. Measurements down to 15 K reveal an increase in transconductance and low-field source-drain conductance. The commonly-observed impact ionisation and its associated gate current were found to decrease significally at low temperature apparently due to a increase in bandgap     

Investigation of the influence of the well and the barrierthicknesses in GaSb/AlSb/GaSb/AlSb/InAs double-barrier interbandtunneling structures

The tunneling currents of GaSb/AlSb/GaSb/AlSb/InAs double-barrier interband tunneling (DBIT) structures were studied experimentally by varying the thickness of the well and the barrier layers systematically. The optimal thicknesses for the GaSb well and the AlSb barriers were found to be 6.5 and 1.0 nm, respectively, to obtain a high peak current density (19 kA/cm²), with a large peak-to-valley ratio of 4. The high peak current in the DBIT structure shows the strong effect of the resonant coherence of the wave function across the double barrier. For the case of a small GaSb well width (3 nm), a drastic reduction of the peak current was observed, an effect suggesting that the electron-wave function in the InAs couples primarily to the quantized light hole state in the GaSb well     

DC and RF performance of LP-MOCVD grownAl0.25Ga0.75As/InxGa1-xAs(x=0.15-0.28) P-HEMT's with Si-delta doped GaAs layer

Si-delta-doped Al_0.25Ga_0.75As/In_xGa_1-xAs (x=0.15-0.28) P-HEMT's, prepared by LP-MOCVD, are investigated. The large conduction band discontinuity leads to 2-DEG density as high as 2.1×10¹²/cm² with an electron mobility of 7300 cm²/V·s at 300 K. The P-HEMT's with 0.7×60 μm gate have a maximum extrinsic transconductance of 380 mS/mm, and a maximum current density of 300 mA/mm. The S-parameter measurements indicate that the current gain and power gain cutoff frequencies are 30 and 61 GHz, respectively, The RF noise characteristics exhibit a minimum noise figure of 1.2 dB with an associated gain of 10 dB at 10 GHz. Due to the efficient doping technique, the electron mobility and transconductance obtained are among the best reported for MOCVD grown P-HEMT's with the similar structure     

Impact ionization suppression by quantum confinement: Effects onthe DC and microwave performance of narrow-gap channel InAs/AlSb HFET's

InAs/AlSb heterostructure field-effect transistors (HFET's) are subject to impact ionization induced short-channel effects because of the narrow InAs channel energy gap. In principle, the effective energy gap to overcome for impact ionization can be increased by quantum confinement (channel quantization) to alleviate impact ionization related nonidealities such as the kink effect and a high gate leakage current. We have studied the effects of quantum well thickness on the dc and microwave performance of narrow-gap InAs/AlSb HFET's fabricated on nominally identical epitaxial layers which differ only by their quantum well thickness. We show that a thinner quantum well postpones the onset of impact ionization and suppresses short-channel effects. As expected, the output conductance g_DS and the gate leakage current are reduced. The f_MAX/f_T ratio is also significantly improved when the InAs well thickness is reduced from 100 to 50 Å. The use of the thinner well reduces the cutoff frequency f_T, the transconductance g_m, and the current drive because of the reduced low-field mobility due to interface roughness scattering in thin InAs/AlSb channel layers: the low-field mobility was μ=21 000 and 9000 cm²/Vs for the 100- and 50-Å quantum wells, respectively. To our knowledge, the present work is the first study of the link between channel quantization, in-plane impact ionization, and device performance in narrow-gap channel HFET's     

Enhancement mode InP MISFET's with sulfide passivation andphoto-CVD grown P3N5 gate insulators

High performance enhancement mode InP MISFET's have been successfully fabricated by using the sulfide passivation for lower interface states and with photo-CVD grown P₃N₅ film used as gate insulator. The MISFET's thus fabricated exhibited exhibited pinch-off behavior with essentially no hysteresis. Furthermore the device showed a superior stability of drain current. Specifically under the gate bias of 2 V for 10⁴ seconds the room temperature drain current was shown to reduce from the initial value merely by 2.9% at the drain voltage of 4 V. The effective electron mobility and extrinsic transconductance are found to be about 2300 cm ²/V·s and 2.7 mS/mm, respectively. The capacitance-voltage characteristics of the sulfide passivated InP MIS diodes show little hysteresis and the minimum density of interface trap states as low as 2.6×10¹⁴/cm² eV has been attained     

Sulfide treated GaAs MISFET's with gate insulator of photo-CVDgrown P3N5 film

Sulfide passivated GaAs MISFET's with the gate insulator of photo-CVD grown P₃N₅ films have been successfully fabricated. The device shows the drain current instability less than 22% for the period of 1.0 s ~1.0×10⁴ s, due to excellent properties of sulfide treated P₃N₅/GaAs interface. The effective electron mobility and extrinsic transconductance of the device are about 1300 cm²/V·sec and 1.33 mS, respectively, at room temperature. To estimate the effects of sulfide treatment on P₃N₅/GaAs interfacial properties, GaAs-MIS diodes are also fabricated     

InAs/AlSb dual-gate HFETs

We report the first implementation of InAs/AlSb dual-gate (DG) HFETs. The devices were fabricated by conventional optical lithography and consist of two electrically distinct 1-μm gates, with a 1-μm intergate separation. The DG-HFETs feature well-behaved, kink-free drain characteristics, and exhibit both high transconductance and low output conductance. We find that DG operation significantly reduces the short-channel effects that have so far plagued InAs/AlSb devices, and increases the maximum allowable drain bias. We estimate that cutoff frequencies as high as 30 GHz-μm may be possible for such devices based on simple equivalent circuit models and previously published experimental data on single-gate InAs/AlSb HFETs     

InAs/AlSb/GaSb resonant interband tunneling diodes andAu-on-InAs/AlSb-superlattice Schottky diodes for logic circuits

Integrated resonant interband tunneling (RIT) and Schottky diode structures, based on the InAs/GaSb/AlSb heterostructure system, are demonstrated for the first time. The RIT diodes are advantageous for logic circuits due to the relatively low bias voltages (~100 mV) required to attain peak current densities in the mid-10⁴ A/cm ² range. The use of n-type InAs/AlSb superlattices for the semiconducting side of Schottky barrier devices provides a means for tailoring the barrier height for a given circuit architecture. The monolithically integrated RIT/Schottky structure is suitable for fabrication of a complete diode logic family (AND, OR, XOR, INV)     

GaAs MESFETs on InP substrates grown using chloride close-proximityreactor system

DC and microwave characteristics of GaAs metal-semiconductor field-effect transistors (MESFETs) on InP grown using the chloride close-proximity reactor (CPR) system are reported. The FETs have an extrinsic maximum transconductance of 210 mS/mm for a drain saturation current of 110 mA/mm, a cutoff frequency of unity current gain of 13 GHz, and a maximum frequency of oscillation of 21 GHz. The dislocation density in a 1.6-μm GaAs layer on InP is 10⁸ cm^-2 measured from cross-sectional transmission electron microscopy (TEM). The full width at half maximum of (400) reflection is 270" for a 3-μm-thick GaAs layer     

An In0.15Ga0.85As/GaAs pseudomorphic single quantum well HEMT

This letter describes high electron mobility transistors (HEMT's) utilizing a conducting channel which is a single In0.15Ga0.85AS quantum well grown pseudomorphically on a GaAs substrate. A Hall mobility of 40 000 cm²/V.s has been observed at 77 K. Shubnikov-de Haas oscillations have been observed at 4.2 K which verify the existence of a two-dimensional electron gas at the In0.15Ga0.85As/GaAs interface. HEMT's fabricated with 2-µm gate lengths show an extrinsic transconductance of 90 and 140 mS/mm at 300 and 77 K, respectively-significantly larger than that previously reported for strained-layer superlattice InxGa1-xAs structures which are nonpseudomorphic to GaAs substrates. HEMT's with 1-µm gate lengths have been fabricated, which show an extrinsic transconductance of 175 mS/mm at 300 K which is higher than previously reported values for both strained and unstrained InxGa1-xAs FET's. The absence of AlxGa1-xAs in these structures has eliminated both the persistent photoconductivity effect and drain current collapse at 77 K.     

Planar-doped n-type InAlAs/InGaAs MODFETs on InP(311)A substratesby molecular beam epitaxy

N-type doping of silicon in InAlAs/InGaAs/InP modulation-doped field effect transistor (MODFET) structures grown by molecular beam epitaxy (MBE) for the (311)A orientation has been achieved by using the planar-doping technique. An electron mobility as high as 50000 cm² V-s with a sheet carrier concentration of 1.9×10¹²/cm² at 77 K is reported. MODFETs with 1.2-μm gate length exhibit an extrinsic transconductance of 400 mS/mm and a maximum drain current of 485 mA/mm. The results are comparable to those of MODFETs grown on (100) InP substrates. The results point to the possibility of making p-n multi layer structures with all-silicon doping     

n-Channel AlSb/GaSb modulation-doped field-effect transistors

We report the first fabrication of a GaSb n-channel modulation-doped field-effect transistor (MODFET) grown by molecular beam epitaxy. The modulation-doped structure exhibits a room temperature Hall mobility of 3140 cm² V⁻¹ s⁻¹ and 77 K value of 16000 cm² V⁻¹ s⁻¹, with corresponding sheet carrier densities of 1.3 × 10¹² cm⁻² and 1.2 × 10¹² cm⁻². Devices with 1 μm gate length yield transconductances of 180 mS mm⁻¹ and output of 5 mS mm⁻¹ at 85 K. The device characteristics indicate that electron transport in the channel occurs primarily via the L-valley of GaSb above 85 K. The effective electron saturation velocity is estimated to be 0.9 × 10⁷ cm s⁻¹. Calculations show that a complementary circuit consisting of GaSb n- and p-channel MODFETs can provide at least two times improvement in performance over AlGaAs/GaAs complementary circuits.     

High performance 0.35 μm gate-length monolithicenhancement/depletion-mode metamorphicIn0.52Al0.48As/In0.53Ga0.47As HEMTs on GaAs substrates

Monolithic integration of enhancement (E)- and depletion (D)-mode metamorphic In_0.52Al_0.48As/In_0.53Ga_0.47 As/GaAs HEMTs with 0.35 μm gate-length is presented for the first time. Epilayers are grown on 3-inch SI GaAs substrates using molecular beam epitaxy. A mobility of 9550 cm²/V-s and a sheet density of 1.12×10^{12 -2} are achieved at room temperature. Buried Pt-gate was employed for E-mode devices to achieve a positive shift in the threshold voltage. Excellent characteristics are achieved with threshold voltage, maximum drain current, and extrinsic transconductance of 100 mV, 370 mA/mm and 660 mS/mm, respectively for E-mode devices, and -550 mV, 390 mA/mm and 510 mS/mm, respectively for D-mode devices. The unity current gain cutoff frequencies of 75 GHz for E-mode and 80 GHz for D-mode are reported