Common Emitter Operation Research Articles

Common Emitter Current and Voltage Gain in III-Nitride Tunneling Hot Electron Transistors

Common-emitter operation was demonstrated in an N-polar tunneling hot electron transistor. Under collector-emitter bias of 7 V, small signal current gain ~1.3, and voltage gain ~4 were simultaneously obtained for transistors with 27.5-nm base. This is the first report of a III-nitride hot electron transistor with small signal current gain and intrinsic voltage gain both greater than unity. The result shows such III-nitride vertical transistors are promising for the next generation of high-frequency amplifiers.

AlGaN/GaN heterojunction bipolar transistors by ammonia molecular beam epitaxy

AbstractWe demonstrate AlGaN/GaN heterojunction bipolar transistors (HBTs) by ammonia molecular beam epitaxy (NH3 MBE). The several benefits offered by NH3 MBE for the growth of GaN based vertical electronic devices are discussed. To obtain good ohmic contacts to the base layer, devices were fabricated with two different processes involving regrowths – regrown base contact (Wafer A) and regrown emitter (Wafer B). Devices on Wafers A and B had similar DC performance. Common emitter (CE) operation with a peak collector current density, JC > 1 kA/cm2 was obtained from devices on both wafers. In CE operation, a current gain (β) of 1.5–3 is observed in devices on both wafers. High base resistance is found to limit the current gain in CE operation, by limiting the base‐emitter bias voltage in the active region of the device. Maximum β values observed from Gummel plots at a fixed base‐collector (BC) bias of zero volts, are β ∼ 15 at JC = 0.88 kA/cm2 for Wafer A and β ∼13.5 at JC = 3 kA/cm2 for Wafer B. In devices on both wafers, variation is observed in the plots of β versus IC (collector current) for devices with the same emitter dimensions and geometry but with different lateral spacing between emitter mesa and base contacts (WEB). Peak β obtained is also observed to vary with WEB. An explanation is provided for the observed behaviour. This work demonstrates the potential of NH3 MBE for the growth of GaN HBTs.

Demonstration of Common–Emitter Operation in AlGaN/SiC Heterojunction Bipolar Transistors

We report here on the fabrication and characterization of new aluminum gallium nitride (AlGaN)/silicon carbide heterojunction bipolar transistors (HBTs). In the HBTs, AlN/GaN short-period superlattice (quasi-AlGaN) was employed as the widegap emitter. We have successfully demonstrated band-offset control and the first common-emitter-mode operation (β ~ 2.7) in the HBTs.

N-Al0.15Ga0.85 N/p-6H–SiC heterostructure and based bipolar transistor

Heterojunction bipolar transistor (HBTs) based on Al0.15Ga0.85 N/6H–SiC heterojunction was fabricated. Room-temperature current–voltage ( I– V) characteristics of n-Al0.15Ga0.85 N/p-6H–SiC emitter–base heterojunction exhibited good rectifying behavior with a forward current 5 × 10 −2 A and reverse current 3 × 10 −9 A at 10 V and −10 V, respectively. Analysis of the temperature dependent I– V characteristics of this heterojunction revealed a barrier height of 1.1 eV. The fabricated n-Al0.15Ga0.85 N/p-SiC/n-SiC bipolar transistor did not exhibit common-emitter operation, however, common-base operation was observed with current gain β = IC/ IB ranging in 75–100.

Operation of Silicon Carbide BJTs Free from Bipolar Degradation

The mechanisms of bipolar degradation in silicon carbide BJTs are investigated and identified. Bipolar degradation occurs as result of stacking fault (SF) growth within the low-doped collector region. A stacking fault blocks vertical current transport through the collector, driving the defective region into saturation. This results in considerable drop of emitter current gain if the BJT is run at a reasonably low collector-emitter bias. The base region does not play any significant role in bipolar degradation. Long-term stress tests have shown full stability of large-area high-power BJTs under minority carrier injection conditions provided the devices are fabricated using low Basal Plane Dislocation (BPD) material. However, an approximately 20% current gain compression is observed for the first 30-60 hours of burn-in under common emitter operation, which is related to instability of surface recombination in the passive base region.

High-temperature characteristics up to 590 °C of a pnp AlGaN/GaN heterojunction bipolar transistor

We investigated the temperature dependence of the common-emitter I-V characteristics of a pnp AlGaN/GaN heterojunction bipolar transistor (HBT) at temperatures ranging from RT to 590 °C. The HBT operated at 590 °C in air with a current gain of 3. Even at 590 °C, the collector-emitter leakage current was as low as 9 μA at the collector-emitter voltage of 40 V. Although there is no significant degradation of the HBT characteristics only by annealing in air at 400 °C for 2 h, the current gain reduced to 30% of the initial one after the common-emitter operation at 400 °C for 2 h.

Analytical Modeling of the Transistor Laser

We derive analytic expressions for the small-signal modulation response of the transistor laser (TL) operating in the common-emitter (CE) and common-base (CB) configurations. We compare the performance (current gain and small-signal modulation bandwidth) of the TL in these two modes of operation. The CE operation results in a small-signal modulation response with the same relaxation oscillation limitations as conventional lasers. The CB configuration shows a bandwidth enhancement due to a bandwidth equalization together with a suppression of the relaxation oscillations. Finally, we show that the small-signal responses of the CB and CE can be approximated by a third-order transfer function.

High-speed (/spl ges/1 GHz) electrical and optical adding, mixing, and processing of square-wave signals with a transistor laser

This letter reports the common-emitter operation (gain beta=DeltaIC/DeltaIB>1, 20degC, IB =36 mA, lambda=970 nm) of a dual-input transistor laser, arranged with a separate base contact on either side of a single emitter, that adds, mixes, and processes high-speed square-wave electrical inputs and delivers separate electrical and optical outputs. Applying a square-wave electrical input X1(t) to one base contact and X2(t) at a second base input, we obtain, with the pulsewidth modulated because of mixing, an electrical output proportional to betatimes[X1(t)+X2(t)] and a laser output tracking the electrical output (hnutimesf[X1(t)+X2(t)]) and exceeding it in bandwidth (pulse sharpness)

Room temperature continuous wave operation of a heterojunction bipolar transistor laser

Continuous wave laser operation at 25°C, with simultaneous electrical gain, of an InGaP–GaAs heterojunction bipolar transistor laser, with AlGaAs optical confining layers and an InGaAs recombination quantum well incorporated into the p-type base region, is demonstrated. At laser threshold (IB=40mA, VCB=0, 25°C), the transistor current gain β=ΔIC∕ΔIB in common-emitter operation changes abruptly (2.3→1.2,β>1), with laser modes developing at wavelength λ∼1006nm. Direct three-port modulation of the transistor laser at 3GHz is demonstrated for a device with a 2.2μm emitter width and a 850μm length between cleaved Fabry–Perot facets (which is the performance of an exploratory device and not near the limits).

Laser operation of a heterojunction bipolar light-emitting transistor

Data are presented demonstrating the laser operation (quasicontinuous, ∼200K) of an InGaP–GaAs–InGaAs heterojunction bipolar light-emitting transistor with AlGaAs confining layers and an InGaAs recombination quantum well incorporated in the p-type base region. Besides the usual spectral narrowing and mode development occurring at laser threshold, the transistor current gain β=ΔIc∕ΔIb in common emitter operation decreases sharply at laser threshold (6.5→2.5,β>1).

Very high voltage operation (>330 V) with high current gain of AlGaN/GaN HBTs

N-p-n Al/sub 0.05/GaN/GaN heterojunction bipolar transistors with a common emitter operation voltage higher than 330 V have been demonstrated using selectively regrown emitters. Devices were grown by metalorganic chemical vapor deposition on sapphire substrates. The n-type emitter was grown selectively on a 100-nm-thick p-base with an 8 /spl mu/m n-collector structure using a dielectric mask. The shallow etch down to the collector mitigates damages induced in the dry etch, resulting a low leakage and a high breakdown. The graded AlGaN emitter results in a common emitter current gain of /spl sim/18 at an average collector current density of up to 1 kA/cm/sup 2/ at room temperature.

High voltage operation (>80 V) of GaN bipolar junction transistors with low leakage

We have demonstrated the high voltage operation of n-p-n GaN bipolar junction transistors using regrown emitters. Devices were grown by metalorganic chemical vapor deposition on sapphire substrates. The n-type emitter was grown selectively on a base-collector p-n junction diode using a dielectric mask. A thin base (1000 Å) was used to increase the current gain over our previous result with a regrown emitter [J. B. Limb, L. McCarthy, P. Kozodoy, H. Xing, J. Ibbetson, Y. Smorchkova, S. P. DenBaars, and U. K. Mishra, Electron. Lett. 35, 19 (1999)]. The base contacts were better than expected despite the use of a thin base. Common emitter operation showing a voltage operation of over 80 V with negligible leakage has been demonstrated. Room temperature current gain was ∼3 corresponding to a current transfer ratio of ∼0.75. This results in a calculated minority carrier lifetime of about 80 pS in the base.

GaN/SiC HBTs and related issues

This paper reviews recent progress in the field of GaN/SiC heterojunction bipolar transistors. Key issues are identified and discussed. These include the comparison of a double-mesa and a selectively grown emitter structure, the evaluation of the GaN/SiC heterojunction and the problems faced when operating the devices in a common-emitter mode. A circuit simulation is presented indicating that common-emitter operation can be obtained for devices with low leakage current and modest gain.

Silicon Auger transistor—New insight into the performance of a tunnel MIS emitter transistor

An experimental study of the silicon tunnel MIS emitter transistor characteristics shows that tunneling hot electrons produce Auger ionization in the collector layer. This effect is responsible for a high value and a multistep sharp rise of current gain and for multistable S-shape collector characteristics in common emitter operation. A possible modification of the transistor structure is a transistor with a metal (or superconducting) base layer. The Auger ionization probability near threshold in Si has been studied by using an Auger transistor structure.

Physical Theory of New Circuit Representation for Junction Transistors

A circuit representation for a junction transistor is derived which places the mechanism of transistor action in evidence. The circuit is a direct interpretation of the diffusion equation and the boundary conditions which include the effects of base width modulation. It is found that the active part of the circuit is independent of frequency. A modification of the circuit for common emitter operation is shown and experimental results are given.