Selfaligned AlGaAs/GaAs HBT grown by MOMBE

The very low parasitic resistance n-p-n GaAs/AlGaAs heterojunction bipolar transistors (HBT) grown by metal organic molecular beam epitaxy (MOMBE) using all gaseous source dopants are reported. The carbon and tin dopants were introduced through the uses of trimethygallium (TMGa) and tetraethyltin (TESn). To achieve the low parasitics, the graded InGaAs emitter cap layer was doped with tin to 5*10/sup 19/ cm/sup -3/ and the doping level in the subcollector was 3*10/sup 18/ cm/sup -3/. The emitter and collector sheet resistances were 25 Omega / Square Operator and 10 Omega / Square Operator , respectively. The 800 AA thick base layer was carbon doped to a level of 7*10/sup 19/ cm/sup -3/. The base contact resistance and sheet resistance were 0.1 Omega mm and 180 Omega / Square Operator , respectively. With a thin AlGaAs surface passivation layer for the emitter-base junction, the common emitter DC current gain was maintained up to 25, even for 2*5 mu m/sup 2/ emitter size devices. The unity short circuit current gain cutoff frequency f/sub T/, and maximum oscillation frequency f/sub max/, were 48 and 63 GHz, respectively.<>     

Millimetre wave performance of carbon-doped-base AlGaAs/GaAs HBTs

AlGaAs/GaAs HBTs with f/sub T/ of 52 GHz and f/sub max/ of 85 GHz have been obtained using a heavily-carbon-doped base layer. The HBT epitaxial layers were prepared by low-pressure MOVPE using carbon tetrachloride as the carbon source. To the author's knowledge, this work reports the first carbon-doped AlGaAs/GaAs HBTs with f/sub T/ and f/sub max/ greater than 50 GHz.<>     

Wideband DHBTs using a graded carbon-doped InGaAs base

We report an InP/InGaAs/InP double heterojunction bipolar transistor (DHBT), fabricated using a mesa structure, exhibiting 282 GHz f/sub /spl tau// and 400 GHz f/sub max/. The DHBT employs a 30 nm InGaAs base with carbon doping graded from 8/spl middot/10/sup 19//cm/sup 3/ to 5/spl middot/10/sup 19//cm/sup 3/, an InP collector, and an InGaAs/InAlAs base-collector superlattice grade, with a total 217 nm collector depletion layer thickness. The low base sheet (580 /spl Omega/) and contact (<10 /spl Omega/-/spl mu/m/sup 2/) resistivities are in part responsible for the high f/sub max/ observed.     

Influences of sulfur passivation on temperature-dependent characteristics of an AlGaAs/InGaAs/GaAs PHEMT

The influences of (NH/sub 4/)/sub 2/S/sub x/ treatment on an AlGaAs/InGaAs/GaAs pseudomorphic high electron mobility transistor (PHEMT) are studied and demonstrated. Upon the sulfur passivation, the studied device exhibits better temperature-dependent dc and microwave characteristics. Experimentally, for a 1/spl times/100 /spl mu/m/sup 2/ gate/dimension PHEMT with sulfur passivation, the higher gate/drain breakdown voltage of 36.4 (21.5) V, higher turn-on voltage of 0.994 (0.69) V, lower gate leakage current of 0.6 (571) /spl mu/A/mm at V/sub GD/=-22 V, improved threshold voltage of -1.62 (-1.71) V, higher maximum transconductance of 240 (211) mS/mm with 348 (242) mA/mm broad operating regime (>0.9g/sub m,max/), and lower output conductance of 0.51 (0.53) mS/mm are obtained, respectively, at 300 (510) K. The corresponding unity current gain cutoff frequency f/sub T/ (maximum oscillation frequency f/sub max/) are 22.2 (87.9) and 19.5 (59.3) GHz at 250 and 400 K, respectively, with considerably broad operating regimes (>0.8f/sub T/,f/sub max/) larger than 455 mA/mm. Moreover, the relatively lower variations of device performances over wide temperature range (300/spl sim/510 K) are observed.     

Performance enhancement by using the n/sup +/-GaN cap layer and gate recess technology on the AlGaN-GaN HEMT fabrication

Due to the low mobility and wide bandgap characteristics of the undoped AlGaN layer used in the conventional AlGaN-GaN HEMT as a cap layer, the RF performance of this device will be limited by its high contact resistance and high knee voltage. In this letter, we propose using the n/sup +/-GaN cap layer and the selective gate recess etching technology on the AlGaN-GaN HEMTs fabrication. With this n/sup +/-GaN instead of the undoped AlGaN as a cap layer, the device contact resistance is reduced from 1.0 to 0.4 /spl Omega//spl middot/mm. The 0.3 /spl mu/m gate-length device demonstrates an I/sub ds,max/ of 1.1 A/mm, a g/sub m,max/ of 220 mS/mm, an f/sub T/ of 43 GHz, an f/sub max/ of 68 GHz, and an output power density of 4 W/mm at 2.4 GHz.     

High-performance, graded-base AlGaAs/InGaAs collector-upheterojunction bipolar transistors using a novel selective area regrowthprocess

Graded-base AlGaAs/InGaAs collector-up heterojunction bipolar transistors (C-up HBTs) were successfully fabricated using a novel selective area regrowth process to reduce the base resistance and their dc and microwave performances were evaluated. The base is compositionally graded to provide a quasi-built-in field which decreases the base transit time for high-frequency response and increases the base transport factor at low-temperature operation. A unity-gain cutoff frequency f_T=55 GHz and a maximum frequency of oscillation f _MAX=74 GHz for the C-up n-p-n HBT, and an f_T=48 GHz and an f_MAX= 39 GHz for the C-up p-n-p HBT were obtained for devices with a 5-μm×10-μm collector area. The nonself-aligned C-up HBT's reported here show great promise for future high-speed C-up complementary bipolar IC's     

Microwave low-noise AlGaAs/InGaAs HBT's with p+-regrownbase contacts

This paper reports low-noise AlGaAs/InGaAs heterojunction bipolar transistors (HBT's) with p⁺-regrown base contacts. To reduce the thermal and shot noises, we have reduced R_B by using a p ⁺-regrown base contact and have reduced τ_B by using a compositionally-graded thin base layer. As a result, F_min values of 0.9, 1.1, 1.2, and 1.6 dB were obtained at 2, 6, 12, and 18 GHz, respectively. These low-noise characteristics of our HBT's show high potential for low-noise application     

A 40-Gb/s preamplifier using AlGaAs/InGaAs HBTs with regrown basecontacts

A preamplifier for 40-Gb/s optical transmission systems incorporating AlGaAs/InGaAs heterojunction bipolar transistors (HBTs) with p⁺ regrown extrinsic base layers is described. The HBTs have a heavily doped regrown p⁺-GaAs layer in the extrinsic base regions and a thin graded InGaAs strained layer for the intrinsic base. Their measured peak f_max is above 200 GHz. The developed preamplifier provides a bandwidth of 38.4 GHz and a transimpedance gain of 41.1 dB Ω. Moreover, the frequency response as an optical receiver has a bandwidth of 32 GHz. These characteristics make the preamplifier suitable for use in a 40-Gb/s optical receiver. These results show that AlGaAs/InGaAs HBTs with p⁺ regrown extrinsic base layers are very promising for use in 40-Gb/s optical transmission systems     

Self-aligned AlGaAs/GaAs HBT with low emitter resistance utilizingInGaAs cap layer

A self-aligned AlGaAs/GaAs heterojunction bipolar transistor (HBT) with an InGaAs emitter cap layer that has very low emitter resistance is described. In this structure, a nonalloyed emitter contact allows the emitter and base electrodes to be formed simultaneously and in a self-aligned manner. The reduction of emitter resistance greatly improves the HBT's transconductance and cutoff frequency. In fabricated devices with emitter dimensions of 2 μm×5 μm, a transconductance-per-unit-area of 16 mS/μm² and a cutoff frequency of 80 GHz were achieved. To investigate high-speed performance, a 21-stage ECL ring oscillator was fabricated using these devices. Propagation delay times as low as 5.5 ps/gate were obtained, demonstrating the effectiveness of this structure     

Electric parameter evolutions against gatelength and bias in ultrashort gate AlGaAs/GaAs HEMTs

The electric parameter evolutions of state of the art ultrashort gate planar doped AlGaAs/GaAs HEMTs are studied against gatelength l/sub g/=0.4-0.1 mu m and bias. The best value of maximum intrinsic transconductance obtained is g/sub m0max/=800 mS/mm at l/sub g/=0.15 mu m and the measured cutoff frequency is f/sub t/=125 GHz at l/sub g/=0.1 mu m.<>     

Reduction of extrinsic base resistance in GaAs/AlGaAs heterojunction bipolar transistors and correlation with high-frequency performance

Improved high-frequency performance in GaAs/AlGaAs heterojunction bipolar transistors (HBT's) by reduction of extrinsic base resistance is demonstrated. A new self-aligned process which is very simple, yet capable of producing 0.25-µm emitter-to-base contact gaps, is described. By the use of AuBe, we have also been able to produce contact resistances to p-type GaAs (p = 5 × 10¹⁸) as low as 1.2 × 10^-7Ω.cm². This is the lowest value reported to p-type GaAs considering the relatively low doping levels used. By employing these techniques, we have produced HBT's with 2.5-µm-wide emitters having current gain cutoff frequencies fTthat appear to be greater than 35 GHz and maximum oscillation frequenciesf_{max}of 22 GHz.     

A 160-GHz f/sub T/ and 140-GHz f/sub MAX/ submicrometer InP DHBT in MBE regrown-emitter technology

We report a 0.7/spl times/8 /spl mu/m/sup 2/ InAlAs-InGaAs-InP double heterojunction bipolar transistor, fabricated in a molecular-beam epitaxy (MBE) regrown-emitter technology, exhibiting 160 GHz f/sub T/ and 140 GHz f/sub MAX/. These initial results are the first known RF results for a nonselective regrown-emitter heterojunction bipolar transistor, and the fastest ever reported using a regrown base-emitter heterojunction. The maximum current density is J/sub E/=8/spl times/10/sup 5/ A/cm/sup 2/ and the collector breakdown voltage V/sub CEO/ is 6 V for a 1500-/spl Aring/ collector. In this technology, the dimension of base-emitter junction has been scaled to an area as low as 0.3/spl times/4 /spl mu/m/sup 2/ while a larger-area extrinsic emitter maintains lower emitter access resistance. Furthermore, the application of a refractory metal (Ti-W) base contact beneath the extrinsic emitter regrowth achieves a fully self-aligned device topology.     

InGaAs-InP metamorphic DHBTs grown on GaAs with lattice-matched device performance and f/sub /spl tau//, f/sub max/>268 GHz

InP-In/sub 0.53/Ga/sub 0.47/As-InP double heterojunction bipolar transistors (DHBTs) were grown on a GaAs substrate using a metamorphic buffer layer and then fabricated. The metamorphic buffer layer is InP - employed because of its high thermal conductivity to minimize device heating. An f/sub /spl tau// and f/sub max/ of 268 and 339 GHz were measured, respectively - both records for metamorphic DHBTs. A 70-nm SiO/sub 2/ dielectric sidewall was deposited on the emitter contact to permit a longer InP emitter wet etch for increased device yield and reduced base leakage current. The dc current gain /spl beta/ is /spl ap/35 and V/sub BR,CEO/=5.7 V. The collector leakage current I/sub cbo/ is 90 pA at V/sub cb/=0.3 V. These values of f/sub /spl tau//, f/sub max/, I/sub cbo/, and /spl beta/ are consistent with InP based DHBTs of the same layer structure grown on a lattice-matched InP substrate.     

InGaAs/InP DHBTs with 120-nm collector having simultaneously high f/sub /spl tau//, f/sub max//spl ges/450 GHz

InP/In/sub 0.53/Ga/sub 0.47/As/InP double heterojunction bipolar transistors (DHBT) have been designed for increased bandwidth digital and analog circuits, and fabricated using a conventional mesa structure. These devices exhibit a maximum 450 GHz f/sub /spl tau// and 490 GHz f/sub max/, which is the highest simultaneous f/sub /spl tau// and f/sub max/ for any HBT. The devices have been scaled vertically for reduced electron collector transit time and aggressively scaled laterally to minimize the base-collector capacitance associated with thinner collectors. The dc current gain /spl beta/ is /spl ap/ 40 and V/sub BR,CEO/=3.9 V. The devices operate up to 25 mW//spl mu/m/sup 2/ dissipation (failing at J/sub e/=10 mA//spl mu/m/sup 2/, V/sub ce/=2.5 V, /spl Delta/T/sub failure/=301 K) and there is no evidence of current blocking up to J/sub e//spl ges/12 mA//spl mu/m/sup 2/ at V/sub ce/=2.0 V from the base-collector grade. The devices reported here employ a 30-nm highly doped InGaAs base, and a 120-nm collector containing an InGaAs/InAlAs superlattice grade at the base-collector junction.     

InGaAs-InP DHBTs for increased digital IC bandwidth having a 391-GHz f/sub /spl tau// and 505-GHz f/sub max/

InP-In/sub 0.53/Ga/sub 0.47/As-InP double heterojunction bipolar transistors (DHBT) have been designed for use in high bandwidth digital and analog circuits, and fabricated using a conventional mesa structure. These devices exhibit a maximum 391-GHz f/sub /spl tau// and 505-GHz f/sub max/, which is the highest f/sub /spl tau// reported for an InP DHBT-as well as the highest simultaneous f/sub /spl tau// and f/sub max/ for any mesa HBT. The devices have been aggressively scaled laterally for reduced base-collector capacitance C/sub cb/. In addition, the base sheet resistance /spl rho//sub s/ along with the base and emitter contact resistivities /spl rho//sub c/ have been lowered. The dc current gain /spl beta/ is /spl ap/36 and V/sub BR,CEO/=5.1 V. The devices reported here employ a 30-nm highly doped InGaAs base, and a 150-nm collector containing an InGaAs-InAlAs superlattice grade at the base-collector junction. From this device design we also report a 142-GHz static frequency divider (a digital figure of merit for a device technology) fabricated on the same wafer. The divider operation is fully static, operating from f/sub clk/=3 to 142.0 GHz while dissipating /spl ap/800 mW of power in the circuit core. The circuit employs single-buffered emitter coupled logic (ECL) and inductive peaking. A microstrip wiring environment is employed for high interconnect density, and to minimize loss and impedance mismatch at frequencies >100 GHz.     

High-performance InGaP/GaAs HBTs with compositionally graded bases grown by solid-source MBE

N-p-n InGaP/GaAs heterojunction bipolar transistors (HBTs) with compositionally graded In/sub x/Ga/sub 1-x/As (Be doped) bases have been successfully grown by solid-source molecular beam Epitaxy (SSMBE) using a gallium phosphide (GaP) decomposition source. In this paper, the dc and RF characteristics of HBTs with different indium mole fractions in the graded In/sub x/Ga/sub 1-x/As base (x:0 /spl rarr/ ;0.1 and x:0 /spl rarr/ 0.05) are measured to investigate optimum-grading profiles. The measured average current gains, /spl beta/s of a control sample, a 10% graded-base sample and a 5% graded-base sample, are 162, 397 and 362, respectively. To our knowledge, these current gains are the highest values ever reported in compositionally graded-base InGaP/GaAs HBTs with a base sheet resistance R/sub sh/ of /spl sim/200 /spl Omega//sq establishing a new benchmark for InGaP/GaAs HBTs. Furthermore, these compositionally graded-base HBTs show higher unity current/gain cutoff frequency, f/sub T/ and maximum oscillation frequency, f/sub max/. Compared to the control sample with the same base thickness, the base transit time /spl tau//sub B/ of the graded sample is reduced by /spl sim/15% to /spl sim/20% by the induced built-in potential, resulting in an increase of f/sub max/ from 16 to 18.5 GHz in a device with an emitter size of 10/spl times/10 /spl mu/m/sup 2/. Additionally, for the 5% graded-base sample, with a 5/spl times/5 /spl mu/m/sup 2/ emitter region, f/sub T/ and f/sub max/ are 16.3 and 33.8 GHz, respectively, under low-level collector current. These results demonstrate that InGaP/GaAs HBTs with In/sub x/Ga/sub 1-x/As graded-base layers (x:0 /spl rarr/ 0.05) have the potential for high-speed analogue to digital converters.     

A 183 GHz f/sub T/ and 165 GHz f/sub max/ regrown-emitter DHBT with abrupt InP emitter

Small-area regrown emitter-base junction InP/In-GaAs/InP double heterojunction bipolar transistors (DHBT) using an abrupt InP emitter are presented for the first time. In a device with emitter-base junction area of 0.7 /spl times/ 8 /spl mu/m/sup 2/, a maximum 183 GHz f/sub T/ and 165 GHz f/sub max/ are exhibited. To our knowledge, this is the highest reported bandwidth for a III-V bipolar transistor utilizing emitter regrowth. The emitter current density is 6/spl times/10/sup 5/ A/cm/sup 2/ at V/sub CE,sat/ = 1.5 V. The small-signal current gain h/sub 21/ = 17, while collector breakdown voltage is near 6 V for the 1500-/spl Aring/-thick collector. The emitter structure, created by nonselective molecular beam epitaxy regrowth, combines a small-area emitter-base junction and a larger-area extrinsic emitter contact, and is similar in structure to that of a SiGe HBT. The higher f/sub T/ and f/sub max/ compared to previously reported devices are achieved by simplified regrowth using an InP emitter and by improvements to the regrowth surface preparation process.     

AlGaAs/GaAs heterojunction bipolar transistors with small size fabricated by a multiple self-alignment process using one mask

A multiple self-alignment process for HBT's using one mask is developed to form emitters, emitter contacts, emitter contact leads, buried small collectors, base contacts, and base contact leads. This process makes it possible to produce HBT's of very small size and to reduce parasitic elements. An AlGaAs/GaAs HBT fabricated by the process, with an emitter 1 × 20/µm²in size and a buried collector by O⁺implantation gives a good performance of ft= 54 GHz and fmax= 42 GHz. The performance may be explained by the reduction of parasitic elements, base transit time, and collector depletion layer transit time.     

Microwave performance of 0.4 mu m gate metamorphic In/sub 0.29/Al/sub 0.71/As/In/sub 0.3/Ga/sub 0.7/As HEMT on GaAs substrate

MBE grown metamorphic In/sub 0.29/Al/sub 0.71/As/In/sub 0.3/Ga/sub 0.7/As/GaAs high electron mobility transistors (HEMTs) have been successfully fabricated. A 0.4 mu m triangular gate device showed transconductance as high as 700 mS/mm at a current density of 230 mA/mm. The measured f/sub T/ was 45 GHz and f/sub max/ was 115 GHz. These high values are, to the authors knowledge, the first reported for submicrometre metamorphic InAlAs/InGaAs/GaAs HEMTs with an indium content of 30%.<>     

Enhanced microwave performance of ion-implanted MESFET with graded GaAs/AlGaAs heterojunctions

Ion-implanted MESFETs have been fabricated on an inverted GaAs/AlGaAs heterostructure. The aluminium concentration in the AlGaAs is graded from 0% at the substrate to 30% at the heterointerface. A maximum extrinsic transconductance of 410 mS/mm is achieved with 0.5 mu m gate devices. This heterojunction ion-implanted FET (HIFET) also exhibits enhanced microwave performance, especially at low drain current, when compared to conventional ion-implanted GaAs MESFETs. At 20% of I/sub dss/, the current gain cutoff frequency f/sub t/ is 40 GHz, which increases up to a maximum value of 47 GHz as the drain current rises. These characteristics of high f/sub t/ and high gain at low current are advantageous for low-noise applications.<>