Characterization of double pulse-doped channel GaAs MESFETs

The fabrication and characterization of a double pulse-doped (DPD) GaAs MESFET grown by organometallic vapor phase epitaxy (OMVPE) are reported. The electron mobility of a DPD structure with a carrier concentration of 3×10¹⁸/cm³ was 2000 cm²/V-s, which is about 20% higher than that of a pulse-doped (PD) structure. Implementing the DPD structure instead of the conventional PD structure as a GaAs MESFET channel, the drain breakdown voltage, current gain cutoff frequency, and maximum stable gain (MSG) increase. The maximum transconductance of 265 mS/mm at a drain current density of 600 mA/mm, a current gain cutoff frequency of 40 GHz, and an MSG of 11 dB at 18 GHz were obtained for a 0.3 μm n⁺ self-aligned DPD GaAs MESFET     

Submicrometer GaAs MESFET with shallow channel and very high transconductance

A 0.5-µm GaAs MESFET with a 25-nm thin channel, 400- mS/mm maximum transconductance, and 580-mS/V.mm K value is presented. This extremely high K value was obtained using an electron-beam fabricated recessed-gate MESFET structure on a highly doped (9.10¹⁷cm^-3) MBE-grown channel layer with 2600-cm²/V.s mobility. The use of thin channels and a buried p-layer also reduced the output conductance and other short-channel effects dramatically. As a result, these scaled MESFET's are very promising for high-speed digital logic circuits.     

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.     

Enhancement-Mode GaAs MOSFETs With an In0.3 Ga0.7As Channel, a Mobility of Over 5000 cm2/V ·s, and Transconductance of Over 475 μS/μm

We present metal-gate high-k-dielectric enhancement-mode (e-mode) III-V MOSFETs with the highest reported effective mobility and transconductance to date. The devices employ a GaGdO high-k (k = 20) gate stack, a Pt gate, and a delta-doped InGaAs/AlGaAs/GaAs hetero-structure. Typical 1-mum gate length device figures of merit are given as follows: saturation drive current, I_d,sat = 407 muA/mum; threshold voltage, V_t = +0.26 V; maximum extrinsic transconductance, g_m = 477 muS/mum (the highest reported to date for a III-V MOSFET); gate leakage current, I_g = 30 pA; subthreshold swing, S = 102 mV/dec; on resistance, R_on = 1920 Omega-mum; I_on/I_off ratio = 6.3 x 10⁴; and output conductance, g_d = 11 mS/mm. A peak electron mobility of 5230 cm²/V. s was extracted from low-drain-bias measurements of 20 mum long-channel devices, which, to the authors' best knowledge, is the highest mobility extracted from any e-mode MOSFET. These transport and device data are highly encouraging for future high-performance n-channel complementary metal-oxide-semiconductor solutions based on III-V MOSFETs.     

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     

The effect of channel boron implants on electron mobility inNMOSFET's

The Hall mobilities and Hall concentrations of channel electrons in boron-implanted NMOSFETs were measured at 77 and 300 K. At both temperatures, the mobilities were found to decrease with increasing implantation dose (10¹¹-10¹² cm^-2) only for electron concentrations <2×10¹² cm^-2, the effect being more pronounced at 77 K. It is suggested that the mobility degradation is mainly due to impurity scattering     

Low ballistic mobility in submicron HEMTs

Ballistic effects in short channel high electron mobility transistors (HEMTs) greatly reduce the field effect mobility compared to that in long gate structures. This reduction is related to a finite electron acceleration time in the channel under the device gate. As an example, the field effect mobility at room temperature in 0.15-μm gate AlGaAs/GaAs HEMTs cannot exceed 3000 cm²/V-s. These predictions are consistent with the values of the field effect mobility extracted from the measured AlGaAs/GaAs HEMT current-voltage characteristics     

High-breakdown AlGaAs/InGaAs/GaAs PHEMT with tellurium doping

The authors report the fabrication and characterisation of an Al _0.43Ga_0.57As/In_0.2Ga_0.8 As/GaAs pseudomorphic HEMT (PHEMT) with high channel conductivity grown by solid source MBE. The high conductivity of the channel is a direct consequence of the high sheet charge and high mobility that has recently been obtained by using tellurium as the n-type dopant in 43% AlGaAs. The device characteristics reflect the resulting reduction in the parasitic resistances of the high channel conductivity. Microwave measurements yield a short-circuit current gain cutoff frequency f_T of 11 GHz and maximum oscillation frequency f_max of 25 GHz. A high gate-drain breakdown voltage of 26 V along with a maximum drain current density of 400 mA/mm obtained in the device illustrate the applicability of this technology in microwave power field effect transistors     

1-μm Enhancement Mode GaAs N-Channel MOSFETs With Transconductance Exceeding 250 mS/mm

In this letter, 1-mum GaAs-based enhancement-mode n-channel devices with channel mobility of 5500 cm²/Vmiddots and g _m exceeding 250 mS/mm have been fabricated. The measured device parameters including threshold voltage V_th, maximum extrinsic transconductance g_m, saturation current I_dss , on-resistance R_on, and gate current are 0.11 V, 254 mS/mm, 380 mA/mm, 4.5 Omegamiddotmm, and < 56 pA for a first wafer and 0.08 V, 229 mS/mm, 443 mA/mm, 4.5 Omegamiddotmm, and < 90 pA for a second wafer, respectively. With an intrinsic transconductance g_mi of 434 mS/mm, GaAs enhancement-mode MOSFETs have reached expected intrinsic device performance     

An anomalous device degradation of SOI narrow width devices causedby STI edge influence

The effects of shallow trench isolation (STI) on silicon-on-insulator (SOI) devices are investigated for various device sizes with three different gate shapes. Both NMOSFETs and PMOSFETs with the channel region butted to the STI show a reduction in mobility (NMOSFETs and PMOSFETs) and an increase of low-frequency noise as the channel width is reduced. In comparison, the devices without the STI-butted channel region show much less variation in mobility for various channel widths. The degradation of MOSFET yield in SOI MOSFETs with the STI is found to be dependent on the device width since the contribution of the interface roughness (or damage) between the STI and the channel formed during the dry etch process becomes significant with the decrease of channel width and the increase of channel length. From the charge-pumping results, the interface state (N_it) generated by the STI process was identified as the cause of the anomalous degradation     

A proposal for a high-speed In0.52Al0.48As/In0.53Ga0.47As MODFET with an (InAs)m(GaAs)msuperlattice channel

In this letter we examine theoretically the potential of an In0.52Al0.48As/In0.53Ga0.47As modulation-doped field-effect transistor in which the usual InGaAs channel is replaced by an (InAs)m(GaAs)msuperlattice with m ≲ 4, extending over 100 ∼ 200 Å from the InAlAs interface. For small m the superlattice bandstructure is essentially the same as that of the alloy and the effects of the very small lattice mismatch are negligible. More importantly, the electrons in the active channel are not expected to suffer any alloy scattering since the channel now has perfect long-range order with no random potential fluctuations. We show that this MODFET has extremely high mobility and its low-temperature mobility can be an order of magnitude higher than that of the conventional InAlAs/InGaAs MODFET. Comparison is also made with the AlGaAs/GaAs MODFET and results indicate that the proposed structure has superior potential performance.     

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     

High-Performance Self-Aligned Bottom-Gate Low-Temperature Poly-Silicon Thin-Film Transistors With Excimer Laser Crystallization

In this letter, high-performance bottom-gate (BG) low-temperature poly-silicon thin-film transistors (TFT) with excimer laser crystallization have been demonstrated using self-aligned (SA) backside photolithography exposure. The grains with lateral grain size of about 0.75 mum could be artificially grown in the channel region via the super-lateral-growth phenomenon fabricated by excimer laser irradiation. Consequently, SA-BG TFT with the channel length of 1 mum exhibited field-effect mobility reaching 193 cm²/V ldr s without hydrogenation, while the mobility of the conventional non-SA-BG TFT and conventional SA top-gate one were about 17.8 and 103 cm²/V ldr s, respectively. Moreover, SA-BG TFT showed higher device uniformity and wider process window owing to the homogenous lateral grains crystallized from the channel steps near the BG edges.     

InGaP/InGaAs HFET with high current density and high cut-offfrequencies

Doped channel pseudomorphic In_0.49Ga_0.51P/In _0.20Ga_0.80As/GaAs heterostructure field effect transistors have been fabricated on GaAs substrate with 0.25 μm T-gates and self-aligned ohmic contact enhancement. By introducing the channel doping and reducing the series resistances, a high current density of 500 mA/mm is obtained in combination with cut off frequencies of f_T=68 GHz and f_max=160 GHz. The channel doping did not affect the RF-performance of the device essentially, which is additionally reflected in noise figures below 1.0 dB with an associated gain of 14.5 dB at 12 GHz     

On the Experimental Determination of Channel Backscattering Characteristics—Limitation and Application for the Process Monitoring Purpose

This paper reports a generalized temperature-dependent channel backscattering extraction method that can self-consistently determine the temperature sensitivity of the low-field mobility and the critical length in nanoscale MOSFETs. Through comparing the gate voltage and temperature dependence, we have shown that assuming constant temperature sensitivity of the low-field mobility and the critical length will result in unphysical backscattering characteristics. We have also investigated the limitation in this self-consistent method and proposed guidelines for experimental extraction. Our results show that channel backscattering is increased for NMOSFETs with higher body doping and HfO₂ dielectric and can be reduced for PMOSFETs when the process-induced uniaxial compressive strain technology is employed. This paper indicates that the self-consistent temperature-dependent method is competent to be routinely used in technology development for the process monitoring purpose.     

InAlAs/InGaAs metamorphic HEMT with high current density and highbreakdown voltage

An In_0.3Al_0.7As/In_0.3Ga_0.7 As metamorphic power high electron mobility transistor (HEMT) grown on GaAs has been developed. This structure with 30% indium content presents several advantages over P-HEMT on GaAs and LM-HEMT on InP. A 0.15-μm gate length device with a single δ doping exhibits a state-of-the-art current gain cut-off frequency F_t value of 125 GHz at V_ds=1.5 V, an extrinsic transconductance of 650 mS/mm and a current density of 750 mA/mm associated to a high breakdown voltage of -13 V, power measurements performed at 60 GHz demonstrate a maximum output power of 240 mW/mm with 6.4-dB power gain and a power added efficiency (PAE) of 25%. These are the first power results ever reported for any metamorphic HEMT     

High-transconductance n-type Si/SiGe modulation-doped field-effecttransistors

The authors report on the fabrication and the resultant device characteristics of the first 0.25-μm gate-length field-effect transistor based on n-type modulation-doped Si/SiGe. Prepared using ultrahigh vacuum/chemical vapor deposition (UHV/CVD), the mobility and electron sheet charge density in the strained Si channel are 1500 (9500) cm²/V-s and 2.5×10¹² (1.5×10¹² ) cm^-2 at 300 K (77 K). At 77 K, the devices have a current and transconductance of 325 mA/mm and 600 mS/mm, respectively. These values far exceed those found in Si MESFETs and are comparable to the best results achieved in GaAs/AlGaAs modulation-doped transistors     

Low field mobility in GaAs ion-implanted FET's

We describe a new technique which allows one to deduce the mobility profiles under the gate of an ion-implanted GaAs MESFET. The technique is based on the measurements of the transconductance and the series resistance at very low drain-to-source voltages. The experimental results show that the mobility drops to about 1000 cm²/V . s at the channel interface from its maximum value of about 2500 cm²/ V . s.     

Comparison of 80-200 nm gate lengthAl0.25GaAs/GaAs/(GaAs:AlAs), Al0.3GaAs/In0.15GaAs/GaAs, and In0.52AlAs/In0.65GaAs/InPHEMTs

In this paper we present a comparative study of the high frequency performance of 80-200 mm gate length Al_0.25GaAs/GaAs/(GaAs:AlAs) superlattice buffer quantum well (QW) HEMTs, Al_0.3GaAs/In_0.15GaAs/GaAs pseudomorphic HEMTs and In_0.52AlAs/In_0.65GaAs/InP pseudomorphic HEMTs. From an experimental determination of the delays associated with transiting both the intrinsic and parasitic regions of the devices, effective electron velocities in the intrinsic channel region under the gate of the HEMT's were extracted. This analysis showed no evidence of any systematic increase in the effective channel velocity with reducing gate length in any of the devices. The effective electron velocity in the channel of the pseudomorphic In_0.65GaAs/InP HEMTs, determined to be at least 2.5×10⁵, was was around twice that of either the Al_0.25GaAs/GaAs quantum well or pseudomorphic In_0.15GaAs/GaAs HEMTs, resulting in 80 nm gate length devices with f_T's of up to 275 GHz. We also show that device output conductance is strongly material dependent. A comparison of the different buffer layers showed that the (GaAs:AlAs) superlattice buffer was most effective in confining electrons to the channel of the Al_0.25GaAs/GaAs HEMTs, even for 80 nm gate length devices. We propose this may be partly due to the presence of minigaps in the superlattice which provide a barrier to electrons with energies of up to 0.6 eV. The output conductance of pseudomorphic In_0.65GaAs/InP HEMTs was found to be inferior to the GaAs based devices as carriers in the channel have greater energy due to their higher effective velocity and so are more difficult to confine to the 2DEG     

Metamorphic InAlAs/InGaAs HEMTs on GaAs substrates with a novelcomposite channels design

We report on fabrication and performance of novel 0.13 μm T-gate metamorphic InAlAs/InGaAs HEMTs on GaAs substrates with composite InGaAs channels, combining the superior transport properties of In_0.52Ga_0.48As with low-impact ionization in the In_0.32Ga_0.68As subchannel. These devices exhibit excellent DC characteristics, high drain currents of 750 mA/mm, extrinsic transconductances of 600 mS/mm, combined with still very low output conductance values of 20 mS/mm, and high channel and gate breakdown voltages. The use of a composite InGaAs channels leads to excellent cut-off frequencies: f_max of 350 GHz and an f_T 160 GHz at V_DS=1.5 V. These are the best microwave frequency results ever reported for any FET on GaAs substrate