Comparison of In0.5Ga0.5P/GaAs single- anddouble-heterojunction bipolar transistors with a carbon-doped base

A comparison of MOCVD-grown, n-p-n In_0.5Ga_0.5P/GaAs single- and double-heterojunction bipolar transistors (SHBTs and DHBTs) with a carbon-doped base is presented. A base doping level of 2.5×10¹⁹ cm^-3 was employed in both device structures, resulting in a base sheet resistance of 500 Ω/sq. Common-emitter current gains as high as 210 and 150 were measured for the SHBTs and DHBTs, respectively. Results of a DC performance optimization study indicate that a 15- and 25-Å undoped set-back layer at the emitter-base junction provides optimal common-emitter current gain. The DHBTs exhibited a 40% improvement in common-base breakdown voltage compared to SHBTs (25 versus 18 V), indicating that In_0.5Ga_0.5P/GaAs DHBTs may prove suitable for power device applications     

InP/InGaAs heterojunction bipolar transistors grown by gas-sourcemolecular beam epitaxy with carbon-doped base

The first N-p-n InP/InGaAs heterojunction bipolar transistors (HBTs) with p-type carbon doping in InGaAs are reported. P-type carbon doping in the InGaAs base has been achieved by gas-source molecular beam epitaxy (GSMBE) using carbon tetrachloride (CCl₄) as the dopant source. The resulting hole concentration in the base was 1×10¹⁹ cm^-3. HBTs fabricated using material from this growth method display good I-V characteristics with DC current gain above 500. This verifies the ability to use carbon doping to make a heavily p-type InGaAs base of an N-p-n HBT     

High-performance carbon-doped base GaAs/AlGaAs heterojunction bipolar transistor grown by MOCVD

High-performance HBTs with a carbon-doped base layer (p=4*10/sup 19/ cm/sup -3/) are reported. The use of carbon as a p-type dopant allows the emitter-base p-n junction to be accurately positioned relative to the heterojunction, and the MOCVD growth method ensures consistency and uniformity of the wafer epitaxial structure. Microwave HBTs with current gains h/sub FE/=50 and f/sub T/ and f/sub max/ values of 42 GHz and 117 GHz, respectively, are reported.<>     

High-performance InP/InGaAs heterojunction bipolar transistors with highly carbon-doped base grown by chemical beam epitaxy

InP/In/sub 0.53/Ga/sub 0.47/As heterojunction bipolar transistors (HBTs) using a highly carbon-doped base are reported. High carbon doping has been achieved by chemical beam epitaxy (CBE). The resulting hole concentration in the carbon-doped base is as high as 7*10/sup 19//cm/sup 3/. To the authors' knowledge, this is the highest doping level reported using carbon. HBTs with a 20 AA spacer layer exhibited nearly ideal I-V characteristics with collector and base current ideality factor of 1.018 and 1.037, respectively. Current gain and breakdown voltage BV/sub CEO/ were 7 and 6 V, respectively.<>     

High-performance Ga0.51In0.49P/GaAs airbridgegate MISFET's grown by gas-source MBE

Ga_0.51In_0.49P/GaAs MISFET's, in which Ga_0.51In_0.49P insulating layer was inserted between the gate metal and the channel layer, were compared with MESFET's experimentally and theoretically in terms of DC and microwave performance. Devices performance were evaluated by varying the thickness of the insulating layer. Wide and flat characteristics of g_m, g_t, and f_max versus drain current (or gate voltage) together with a high maximum current density (above 610 mA/mm) were achieved for devices with insulating layer thickness of 50 mn and 100 mm. Moreover, the maximum values of J_t's and f_max 's for a 1-μm gate length device both occurred when t was between 50 and 100 mn. We also observed that parasitic capacitances and gate leakage currents were minimized by using the airbridge gate structure, and thus high-frequency and breakdown characteristics were greatly improved, These results demonstrate that Ga_0.51In_0.49P/GaAs airbridge gate MISFET's with insulating layer thickness between 50 and 100 mn were very suitable for microwave high-power device applications     

Atomic layer epitaxy grown heterojunction bipolar transistor havinga carbon-doped base

The fabrication of a GaAs/AlGaAs heterojunction bipolar transistor (HBT) having a carbon-doped base is reported. The low diffusion coefficient of carbon makes it attractive for HBT applications since it will prevent out diffusion. The base was grown by atomic layer epitaxy (ALE), from a TMG (trimethylgallium) source that allowed the incorporation of carbon into the layer from the partially related TMG metal carbide. HBTs with common-emitter current gains of 100 were obtained at current densities of 1300 A-cm^-2     

AlGaAs/GaAs pnp heterojunction bipolar transistor with carbon-doped collector and emitter grown by atomic layer epitaxy

The first AlGaAs/GaAs pnp heterojunction bipolar transistor (HBT) grown entirely by atomic layer epitaxy (ALE) is reported. Carbon was used as the p-type dopant in the emitter and collector. The use of carbon, with its low diffusivity and the potential for very heavy doping, will lead to reduced emitter and collector resistances in a pnp structure. For the devices reported here, a common emitter current gain over 100 was obtained, with good I/V characteristics.<>     

25.5% efficient Ga0.35In0.65P/Ga0.83In0.17As tandem solar cells grown on GaAs substrates

Theoretical calculations predict a higher power conversion efficiency for the combination of Ga_0.35In_0.65P and Ga_0.83In_0.17As in a tandem solar cell, compared to the more commonly used Ga_0.51In_0.49P/GaAs approach. A record conversion efficiency of 21.6% (AM1.5 g) was recently achieved for a 1.18 eV Ga_0.83In_0.17As solar cell, grown lattice-mismatched to the GaAs substrate material. This paper reports on the device characteristics of first Ga_0.35In_0.65P/Ga_0.83In_0.17As tandem solar cells based on this very promising GaInAs material. A high quantum efficiency, comparable to the lattice-matched Ga_0.51In_0.49P on GaAs approach was achieved. A power conversion efficiency of 25.5% was measured under AM1.5d spectral conditions     

High-current-gain Ga0.51In0.49P/GaAsheterojunction bipolar transistor grown by gas-source molecular beamepitaxy

A Ga_0.51In_0.49P/GaAs heterojunction bipolar transistor (HBT) grown on a (100) substrate by gas-source molecular beam epitaxy (GSMBE) was fabricated. A common-emitter DC current gain exceeding 1580 (differential gain >2100) and an offset voltage as small as 120 mV were achieved. The results demonstrate that high current gain and small offset voltage can be maintained without the need of grading the emitter/base junction in the Ga_0.51In_0.49 P/GaAs system because its valence-band discontinuity is larger than its conduction-band discontinuity     

High-breakdown-voltage Ga0.51In0.49P channelMESFET's grown by GSMBE

The first Ga_0.51In_0.49P channel MESFETs grown on a (100) GaAs substrate by GSMBE have been fabricated. A high gate-to-drain breakdown voltage of 42 V with a high maximum current density (320 mA/mm) was achieved. This result demonstrates that high-breakdown voltage could be attained by using Ga_0.51In _0.49P as the channel material. We also measured a high-maximum oscillation frequency (f_max) of 30 GHz for a 1.5 μm gate-length device. This value is quite high compared with other high-breakdown-voltage GaAs MESFET's or MISFET's with the same gate length     

Novel GaAs heterojunction bipolar transistors usingIn0.5Al0.5P as emitter

We report the fabrication and characterization of the first single and double In_0.5Al_0.5P/GaAs heterojunction bipolar transistors (HBT's). These HBT's are grown by gas-source molecular beam epitaxy. The In_0.5Al_0.5P/GaAs heterostructure has the largest valence band discontinuity among all Ill-V semiconductor heterojunctions lattice-matched to GaAs. Common-emitter dc current gains as high as 300 and 400 are measured for SHBT's and DHBT's, respectively, with base doping of 1×10¹⁹ cm^-3. The corresponding offset voltage is 80 and 120 mV, respectively. These results demonstrate the advantages of the In_0.5Al_0.5 P/GaAs band alignment and make the new HBT's attractive candidates for high-speed digital circuit applications     

Choice of epitaxial structure to promote performance and uniformityof GaAs/AlGaAs heterojunction bipolar transistors grown by MOVPE

Numerical simulations with a one-dimensional physical device model are used to investigate the importance of the design of the emitter and base regions of n-p-n GaAs/AlGaAs HBT structures. A structure of optimum gain and speed is determined together with limits for the variations of the aluminum gradings and doping placement. The simulations show that the edge of the base doping on the emitter side has to be controlled within a few nanometers to avoid serious degradations of the current gain and the cutoff frequency. Variation in the position of the base doping relative to the aluminum gradings is a plausible source of the spread in current gain observed in measurements of devices made by metalorganic vapor-phase epitaxy (MOVPE). It is predicted that longer emitter aluminum gradings will reduce the sensitivity to these variations together with the peak values of gain and speed. It is suggested that the grading length be chosen as a compromise between performance and uniformity depending on the accuracy of the manufacturing method and the demands of the application     

High-frequency performance of MOVPE npn AlGaAs/GaAs heterojunction bipolar transistors

Base doping densities near 10/sup 20/ cm/sup -3/ and emitter doping densities near 7*10/sup 17/ cm/sup -3/ have been achieved in MOVPE HBT structures and combined with self-aligned processing resulting in f/sub max/=94 GHz and f/sub t/=45 GHz. To the authors' knowledge, these are the first MOVPE HBTs demonstrated to operate at millimetre-wave frequencies.<>     

Heterostructure bipolar transistor employing carbon-doped base grown with trimethyl-Ga and arsine

The investigation of an AlGaAs/GaAs HBT in which a heavily carbon doped base is grown by chemical beam epitaxy using trimethyl-Ga is reported. A planar technique which reduces surface recombination has been employed for selectively contacting the base region. A base width of 1000 AA and a high doping level of 7*10/sup 19/ cm/sup -3/ is used. The sheet resistance of the base is less than 100 Omega / Square Operator . This transistor has a maximum current gain of 25 at a current density of 1.3*10/sup 3/ A/cm/sup 2/.<>     

Resonant tunnelling in Ga0.47In0.53As/InPdouble-barrier structures grown by AP-MOCVD

Reports the first observation of negative-differential resistance in Ga_0.47In_0.53As/InP double-barrier structures grown by AP-MOCVD. The devices exhibit the largest peak/valley current ratios seen in this system; 1.2:1 (2.8:1) and 3.0:1 (5.5:1) at 77 K (4.2 K) for the n=1 and n=2 resonances respectively     

650-Å self-aligned-gate pseudomorphicAl0.48In0.52As/Ga0.2In0.8Ashigh electron mobility transistors

The authors report on the design and fabrication of a 650-Å self-aligned-gate pseudomorphic Al_0.48In_0.52As/Ga _0.2In_0.8As high electron mobility transistor (HEMT) with a state-of-the-art current gain cutoff frequency of over 300 GHz. This work clearly demonstrates the potential of sub-0.1-μm gate-length HEMTs for near-future microwave and millimeter-wave applications     

InP/In0.53Ga0.47As heterojunction bipolartransistors with a carbon-doped base grown by MOCVD

InP/In_0.53Ga_0.47As heterojunction bipolar transistors (HBTs) utilizing a carbon-doped base have been demonstrated. The devices were grown by low-pressure metalorganic chemical vapor deposition (LP-MOCVD) using carbon tetrachloride (CCl₄) as the p-type dopant source. These devices exhibit a DC common-emitter current gain of 50 and an emitter-base junction ideality factor of 1.29 in a structure for which no undoped spacer layer was employed at the emitter-base junction. These preliminary results suggest that C-doping of In_0.53Ga_0.47As may be a suitable alternative to Zn in MOCVD-grown InP/In_0.53Ga_0.47As HBTs     

Enhancement mode metamorphicAl0.67In0.33As/Ga0.66In0.34As HEMT on GaAs substrate with high breakdown voltage

This paper presents original and experimental results provided by E-mode Al_0.67In_0.33As/Ga_0.66In_0.34 As metamorphic HEMT. The devices exhibit good dc and rf performances. The 0.4 μm gate length devices have saturation current density of 355 mA/mm at +0.6 V gate-to-source voltage. The Schottky characteristic is a typical reverse gate-to-drain breakdown voltage of -16 V. It is the first time, to our knowledge, that gate current issued from impact ionization have been observed in these devices versus gate to drain extension. These results are the first reported for E-mode Al _0.67In_0.33As/Ga_0.66In_0.34As MM-HEMTs on GaAs substrate     

Ga0.51In0.49P/GaAs HEMT's exhibiting goodelectrical performance at cryogenic temperatures

The DC and microwave characteristics of Ga_0.51In_0.49P/GaAs HEMTs grown by metalorganic chemical vapor deposition (MOCVD) are presented. Devices with 1-μm-long gates show transconductances of 163 and 213 mS/mm at 300 and 77 K, respectively. Their maximum cutoff frequency is 17.8 GHz. Deep traps in the doped layer are evaluated at low temperature by the threshold voltage shift and current collapse phenomena. GaInP/GaAs HEMTs show no current collapse and have almost zero threshold voltage shift compared to AlGaAs/GaAs and InAlAs/InGaAs where the corresponding values are 0.5 and 0.25 V, respectively