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     

InP/InGaAs HBTs with n+-InP contacting layers grown byMOMBE using SiBr4

InP/InGaAs heterojunction bipolar transistors (HBTs) with low resistance, nonalloyed TiPtAu contacts on n⁺-InP emitter and collector contacting layers have been demonstrated with excellent DC characteristics. A specific contact resistance of 5.42×10^-8 Ω·cm², which, to the best of our knowledge, is the lowest reported for TiPtAu on n-InP, has been measured on InP doped n=6.0×10¹⁹ cm^-3 using SiBr₄. This low contact resistance makes TiPtAu contacts on n-InP viable for InP/InGaAs HBTs     

A high-gain GaAs/AlGaAs n-p-n heterojunction bipolar transistor on(100) Si grown by molecular beam epitaxy

High-gain GaAs/AlGaAs n-p-n heterojunction bipolar transistors (HBT's) on Si substrates grown by molecular beam epitaxy (MBE) have been fabricated and tested. In this structure, an n⁺-InAs emitter cap layer was grown in order to achieve a nonalloyed ohmic contact. Typical devices with an emitter dimension of 50×50 μm² exhibited a current gain as high as 45 at a collector current density of 2×10³ A/cm² with an ideality factor of 1.4. This is the highest current gain reported for HBT's grown on Si substrates. Breakdown voltages as high as 10 and 15 V were observed for the emitter-base and collector-base junctions respectively. The investigation on devices with varying emitter dimensions demonstrates that much higher current gains can be expected     

Low emitter resistance GaAs based HBT's without InGaAs caps

Low emitter resistance is demonstrated for AlGaAs/GaAs heterojunction bipolar transistors using Pd/Ge contacts on a GaAs contact layer. The contact resistivity to 2-10×10¹⁸ cm ^-3 n-type GaAs is 4-1×10^-7 Ω-cm² . These are comparable to contact resistivities obtained with non-alloyed contacts on InGaAs layers. The non-spiking Pd/Ge contact demonstrates thermal stability and area independent resistivity suitable for scaled devices. The substitution of Pd/Ge for AuGe/Ni GaAs emitter and collector contacts reduced by an order of magnitude the emitter-base offset voltage at high current densities and increased f_t by more than 15% with significantly improved uniformity for devices with 2 and 2.6 μm wide emitters having lengths two, four and six times the width     

Heterostructure devices using self-aligned p-type diffused ohmiccontacts

Describes the use of a p-type refractory ohmic contact in ohmic self-aligned devices. The contacts are based on self-aligned diffusion of zinc-doped tungsten film. The diffusion is nearly isotropic in the vicinity of silicon nitride sidewalls, allowing self-alignment of ohmic contacts with emitters and gates. Low-resistance contacts (<10^-6 Ω·cm²) are formed both to GaAs and GaAlAs, and the lifetime of the diffused region is superior to that obtained from implantation. Heterostructure bipolar transistors (HBTs) showing high current gains (⩾50 at 2×10³ A·cm^-2 and ⩾200 at 1×10⁵ A·cm^-2 with micrometer-sized emitter widths) and p-channel GaAs gate heterostructure field-effect transistors (HFETs) showing high transconductances (78 mS/mm at 2.2-μm gate length) have been fabricated using this contact     

Performance enhancement of GaInP/GaAs heterojunction bipolarphototransistors using dc base bias

GaInP-GaAs heterojunction bipolar phototransistors grown by metal organic vapor phase epitaxy (MOVPE) and operated with frontside optical injection through the emitter are reported with high optical gain (<88) and record high frequency performance (28 GHz). Heteropassivation of the extrinsic base surface is employed using a depleted GaInP emitter layer between the nonself-aligned base contact and the emitter mesa. The phototransistor's performance is shown to improve with increasing dc base bias in agreement with predictions of a recently reported Gummel-Poon model. Experimental results are reported for devices with optical active areas of 10×10 μm², 20×20 μm², and 30×30 μm², with peak measured cutoff frequencies of 28.5, 23.1, and 18.5 GHz, respectively, obtained at collector current densities between 2×10 ³ and 6×10³ A/cm²     

Fully-planar AlGaAs/GaAs HBT's achieved by selective CBE regrowth

This paper describes a novel fully planar AlGaAs/GaAs heterojunction bipolar transistor (HBT) technology using selective chemical beam epitaxy (CBE). Planarization is achieved by a selective regrowth of the base and collector contact layers. This process allows the simultaneous metallization of the emitter, base and collector on top of the device. For the devices with an emitter-base junction area of 2×6 μm² and a base-collector junction area of 14×6 μm², a current gain cut off frequency of 50 GHz and a maximum oscillation frequency of 30 GHz are achieved. The common emitter current gain h_FE is 25 for a collector current density J_c of 2×10⁴ A/cm²     

Extremely high peak specific transconductance AlGaAs/GaAsheterojunction bipolar transistors

Self-aligned AlGaAs/GAs heterojunction bipolar transistors with peak specific transconductances as high as 25 mS/μm² of emitter area are discussed. These are the highest specific transconductances ever reported for a bipolar transistor. These devices, which contain no indium in the emitter, display specific parasitic emitter resistances of less than 1×10^-7 Ω-cm². This low parasitic resistance is attributed to an improved n-type contact technology, in which a molybdenum diffusion barrier and a plasma-enhanced chemical vapor deposition SiO₂ overlayer are used to achieve low specific contact resistivities     

Planarization of emitter-base structure of heterojunction bipolartransistors by doping selective base contact and nonalloyed emittercontact

The authors report an n-p-n heterojunction bipolar transistor (HBT) with a planar (and thus passivated) emitter-base structure fabricated using a simple, low-temperature technique. They use a nonalloyed emitter contact facilitated by δ-doping grown at the surface of the sample, so that the cap layer is only 75 Å thick. The base is contacted by depositing Au-Zn or Au-Be on the surface and alloying at 420°C for 10 s, resulting in an ohmic contact with the base and rectifying contact with the emitter. The authors present large-emitter area (50-μm diameter) HBTs with homogeneous-doped bases (gain of 170) and δ-doped bases (10¹⁴ cm^-2, gain of 20). Upon reducing the emitter size of the latter to 3×8 μm the gain increased to 30, demonstrating excellent surface passivation     

Low-resistance bandgap-engineeredW/Si1-xGex/Si contacts

Bandgap-engineered W/Si_1-xGe_x/Si junctions (p⁺ and n⁺) with ultra-low contact resistivity and low leakage have been fabricated and characterized. The junctions are formed via outdiffusion from a selectively deposited Si_0.7Ge _0.3 layer which is implanted and annealed using RTA. The Si _1-xGe_x layer can then be selectively thinned using NH₄OH/H₂O₂/H₂O at 75°C with little change in characteristics or left as-deposited. Leakage currents were better than 1.6×10^-9 A/cm² (areal), 7.45×10^-12 A/cm (peripheral) for p⁺/n and 3.5×10^-10 A/cm² (peripheral) for n⁺/p. W contacts were formed using selective LPCVD on Si_1-xGe_x. A specific contact resistivity of better than 3.2×10^-8 Ω cm² for p ⁺/n and 2.2×10^-8 Ω cm² for n⁺/p is demonstrated-an order of magnitude n⁺ better than current TiSi₂ technology. W/Si_1-xGe _x/Si junctions show great potential for ULSI applications     

Experimental values for the hole diffusion coefficient andcollector transit velocity in P-n-p AlGaAs/GaAs HBTs

The diffusion coefficient (D_h) and a value for the collector velocity (v_h) of holes in AlGaAs/GaAs P-n-p HBTs (heterojunction bipolar transistors) were obtained from high-frequency measurements on structures with different base and collector widths. Quantities for D_h and v _h of 5.6 cm²/s and 5.5×10⁶ cm/s, respectively, were obtained by plotting the total emitter-collector delay versus inverse emitter current and extrapolating the data to infinite emitter current to obtain the base and collector transit delays. An f_t and f_max as high as 15 and 29 GHz, respectively, were obtained for non-self-aligned (1-μm emitter mesa/base contact separation) devices with a 2.6-μm×10-μm emitter     

Symmetric P-n-P InAlAs/InGaAs double-heterojunction bipolartransistors fabricated with Si-ion implantation

The authors have successfully fabricated symmetric P-n-P InAlAs/InGaAs double-heterojunction bipolar transistors (DHBTs) using self-aligned Si-ion implantation and refractory emitter contacts with current gains of 115 and 30 in the emitter-up and the emitter-down configurations, respectively. Two thin Be-doped In_0.53Ga_0.47As layers inserted on both sides of base lead to the excellent I-V characteristics. The authors have shown that hole injection from the external portions of the emitter should be suppressed by a factor of 10^-5 to 10^-3 at a collector current density of about 10³ A/cm² , which is much smaller than that of N-p-n GaAs/AlGaAs HBTs and DHBTs are promising devices for applications to circuits with low power dissipation     

Process and device characterization for a 30-GHz fT submicrometer double poly-Si bipolar technology using BF2-implanted base with rapid thermal process

Process and device parameters are characterized in detail for a 30-GHz f_T submicrometer double poly-Si bipolar technology using a BF₂-implanted base with a rapid thermal annealing (RTA) process. Temperature ramping during the emitter poly-Si film deposition process minimizes interfacial oxide film growth. An emitter RTA process at 1050°C for 30 s is required to achieve an acceptable emitter-base junction leakage current with an emitter resistance of 6.7×10^-7 Ω-cm², while achieving an emitter junction depth of 50 nm with a base width of 82 nm. The primary transistor parameters and the tradeoffs between cutoff frequency and collector-to-emitter breakdown voltage are characterized as functions of base implant dose, pedestal collector implant dose, link-base implant dose, and epitaxial-layer thickness. Transistor geometry dependences of device characteristics are also studied. Based on the characterization results for poly-Si resistors, boron-doped p-type poly-Si resistors show significantly better performance in temperature coefficient and linearity than arsenic-doped n-type poly-Si resistors     

AlGaAs/Ge/GaAs heterojunction bipolar transistors grown bymolecular beam epitaxy

An N-Al_0.22Ga_0.78As emitter, p-Ge base, and n-GaAs collector (AlGaAs/Ge/GaAs) heterojunction bipolar transistor (HBT) in the emitter-up configuration grown by molecular beam epitaxy is discussed. Devices exhibited common-emitter current gains of as high as 300 at a collector current density of 2000 A/cm² and a collector voltage of 4 V. As the device area is reduced from 50×50 to 10×40 μm, the current gain did not show significant changes, suggesting a low surface recombination velocity in the Ge base     

Optimization of silicon bipolar transistors for high current gainat low temperatures

Bipolar transistors designed specifically for operation at liquid-nitrogen (LN₂) temperature are discussed. It is found that for high-gain LN₂ bipolar transistors, the emitter concentration should be around 5×10¹⁸ cm^-3. Compensating impurities in the base should be kept to minimum. Test bipolar transistors with polysilicon emitter contacts were fabricated using these criteria. The devices show very little current degradation between room temperature and 77 k. Polysilicon emitter contacts are also shown to be somewhat more effective at lower temperatures     

An (Al,Ga)As/GaAs heterostructure bipolar transistor with nonalloyed graded-gap ohmic contacts to the base and emitter

Graded regions of n-(Ga,In)As and p-Ga(As,Sb) were incorporated side-by-side as emitter and base contacts, respectively, into an n-p-n (Al,Ga)As/GaAs heterostructure bipolar transistor (HBT). The process involved two separate molecular beam epitaxy (MBE) growths, leading to base contact regions that were self-aligned to the emitter mesas. The devices could be easily probed with pressure contacts even prior to any metallization, and excellent characteristics were obtained after final metallization. Contact resistivities of 5 × 10^-7and 3 × 10^-6Ω.cm²were measured for n- and p-type graded-gap ohmic contact structures, respectively.     

Self-alignedIn0.52Al0.48As/In0.53Ga0.47As heterojunction bipolar transistors with graded interface onsemi-insulating InP grown by molecular beam epitaxy

A self aligned In_0.52Al_0.48As/In_0.53 Ga_0.47As double heterojunction bipolar transistor (HBT) with a graded heterointerface has been grown by molecular-beam epitaxy (MBE) and tested. The DC characteristics of HBT structures with a compositionally graded junction using a linear graded In_0.53Ga_0.47-xAl_xAs between two ternary layers were investigated. Typical quaternary graded devices with an emitter dimension of 50×50 μm² exhibited a current gain as high as 1260, as compared to 800 for abrupt devices, at a collector current density of 2.8×10³ A/cm²     

Design study of AlGaAs/GaAs HBTs

The frequency performance of AlGaAs/GaAs heterojunction bipolar transistors (HBTs) having different layouts, doping profiles, and layer thicknesses was assessed using the BIPOLE computer program. The optimized design of HBTs was studied, and the high current performances of HBTs and polysilicon emitter transistors were compared. It is shown that no current crowding effect occurs at current densities less than 1×10⁵ A/cm² for the HBT with emitter stripe width S_E<3 μm, and the HBT current-handling capability determined by the peak current-gain cutoff frequency is more than twice as large as that of the polysilicon emitter transistor. An optimized maximum oscillation frequency formula has been obtained for a typical process n-p-n AlGaAs/GaAs HBT having base doping of 1×10 ¹⁹ cm^-3     

HEMT with nonalloyed ohmic contacts using n+-InGaAs cap layer

We have investigated nonalloyed ohmic contacts on HEMT's using a highly conductive n⁺-InGaAs layer. The minimum specific contact resistance obtained was 4.8 × 10^-7Ω.cm², and the IV characteristics were equal to or better than those of conventional HEMT's with alloyed ohmic contacts. The maximum transconductances of a nonalloyed ohmic HEMT were 240 mS/mm at 300K and 340 mS/mm at 88K for a gate length of 1.1 µm. We conclude that it is not necessary for HEMT's with two-dimensional electron gas (2DEG) channels to have alloyed ohmic contacts, because the tunneling conduction is significant at the n-GaAs/n-AlGaAs/undoped GaAs double heterojunction.     

High frequency performance of SiC heterojunction bipolartransistors

A compact heterojunction bipolar transistor (HBT) model was employed to simulate the high frequency and high power performances of SiC-based bipolar transistors. Potential 6H-SiC/3C-SiC heterojunction bipolar transistors (6H/3C-HBT's) at case temperatures of 27°C (300 K) through 600°C (873 K) were investigated. The high frequency and high power performance was compared to AlGaAs/GaAs HBT's. As expected, the ohmic contact resistance limits the high frequency performance of the SiC HBT. At the present time, it is only possible to reliably produce 1×10^-4 Ω-cm² contact resistances on SiC, so an f_T of 4.4 GHz and an f_max of 3.2 GHz are the highest realistic values. However, assuming an incredibly low 1×10^-6 Ω-cm² contact resistance for the emitter, base, and collector terminals, an f_T of 31.1 GHz and an f_max of 12.7 GHz can be obtained for a 6H/3C-SiC HBT