Takeshi Tomioka

1.5 V Low-Voltage Microwave Power Performance of InAlAs/InGaAs Double Heterojunction Bipolar Transistors

In this paper, we report the first demonstration of microwave power performance of InAlAs/InGaAs double heterojunction bipolar transistors (DHBTs) obtained at an extremely low operating voltage of 1.5 V. In order to obtain a high output power (P out) at a low operating voltage, we used DHBTs rather than single heterojunction bipolar transistors (SHBTs) and thus reduced the offset voltage (V CE,offset). We obtained a much lower V CE,offset of 50 mV for the DHBT than that of 300 mV for a SHBT. At a low operation voltage of 1.5 V, the DHBT exhibited a P out of 20.6 dBm with a power added efficiency (η add) of 36.6% and a power gain (G a) of 8.5 dB biased for class-B operation at 1.9 GHz. The high-speed performance of the DHBT are a unity cutoff frequency (f T) of 76 GHz and a maximum oscillation frequency (f max) of 157 GHz. We also studied the reliability of DHBTs by conducting a 1000-hour accelerated life test. The InGaAs HBTs had a lifetime of 2×106 h at a junction temperature of 125°C with an activation energy of 0.95 eV.

Current status of reliability of InGaP/GaAs HBTs

Abstract We review the current status of two major reliability issues in GaAs-based heterojunction bipolar transistors (HBTs), particularly InGaP/GaAs HBTs: degradation in current gain (β) and variation of turn-on voltage ( V be ). In the case of AlGaAs/GaAs HBTs, the β gradually decreased, then drastically degraded. After degradation, the device exhibits an increase in base current I b , which has an ideality factor n∼ 2 in the Gummel plot. The activation energy for the degradation was estimated to be 0.6 ± 0.1eV. However, in InGaP/GaAs HBTs, much higher reliability than in AlGaAs/GaAs HBTs was achieved though the degradation mode is similar. The estimated E a and time to failure for InGaP/GaAs HBTs are 2.0 ± 0.2eV and 10 6 h at T j = 200°C, respectively, which are the highest values ever reported. We also review previously proposed degradation mechanisms for GaAs-based HBTs; hydrogen reactivation, microtwin-like defect formation, dark defect formation and carbon precipitation. TEM observation of a degraded InGaP/GaAs HBT indicated that there are at least two possible degradation mechanisms: formation of carbon precipitates in the base region and migration of metallic impurities from the base electrode to the base region. The second issue is concerned with the exponential increase in V be with operating time. The mechanism for the increase in V be was clarified based on reactivation of passivated carbon acceptors in the base region during operation. If the device suffers from H + isolation, V be decreases rapidly at the initial stage, then exponentially increases. The first stage of V be variation can be explained by fact that a high density of hydrogen atoms migrating from the region to the intrinsic base region, passivate the carbon atoms at the initial stage. From these results, one can expect that the use of He + as an implant instead of H + can solve this problem.

Suppression of Beryllium Diffusion by Incorporating Indium in AlGaAs for HBT Applications using Molecular Beam Epitaxy

We developed a molecular beam epitaxy technique to suppress Be diffusion by incorporating In in the AlGaAs epilayer. Diffusion coefficients of Be-doped Iny(Al0.1Ga0.9)1-yAs (p: 7×1019 cm-3) grown at 600°C were reduced from 1×10-14 cm2/s to 2×10-15 cm2/s when the InAs mole fraction y was increased from 0 to 0.07, indicating that compressive stress in the epilayer caused by incorporating In plays an important role in suppressing Be diffusion. We fabricated a heterojunction bipolar transistor with a 100-nm-thick p+-In0.055(AlxGa1-x)0.945As base layer (x: 0 to 0.1), and obtained a DC current gain of 27.

Suppression of Be diffusion in molecular‐beam epitaxy AlGaAs by the incorporation of In for heterojunction bipolar transistor applications

We report for the first time on the suppression of Be diffusion in molecular‐beam epitaxy Al0.1Ga0.9As by incorporating In into the epilayer. The minimum diffusion coefficient of Be‐doped Iny(Al0.1Ga0.9)1−yAs layers with a carrier concentration of 7×1019 cm−3 and an InAs mole fraction of 0.07 grown at 600 °C was about 2×10−15 cm2/s, which is five times smaller than that without In incorporation. The photoluminescence intensity of the layers drastically decreased above a value of y of 0.05, probably due to crystal degradation resulting from misfit dislocations. A heterojunction bipolar transistor with a 100 nm‐thick p+In0.055 (AlxGa1−x)0.945As base layer (Al graded composition x: 0 to 0.1, emitter area: 4×5 μm2) yielded a dc current gain of 27 at a collector current of 8 mA.

InAlAs/InGaAs double heterojunction bipolar transistors with a collector launcher structure for high-speed ECL applications

Summary form only given. The authors report the demonstration of high-speed ECL (emitter coupled logic) circuits using InAlAs/InGaAs double-heterojunction bipolar transistors (DHBTs). These DHBTs use a launcher structure in the collector to reduce the collector transit time. The DHBTs achieve the cutoff frequencies of f/sub T/=64 GHz and f/sub max/=54 GHz and hold a breakdown voltage about three times that of conventional InGaAs single-heterojunction bipolar transistors. A 1/4-frequency divider with bilevel ECL gates fabricated using these DHBTs operated at up to 11.9 GHz with a supply voltage of 3.5 V. The total power consumption was 255 mW. The novel collector structure produces high-speed and high-breakdown-voltage DHBTs, enabling high-speed digital applications of InGaAs-based HBTs.<<ETX>>

High current gain InGaP/GaAs heterojunction bipolar transistors grown by multi-wafer gas-source molecular beam epitaxy system

Abstract We report for the first time on the high quality and highly uniform InGaP/GaAs heterojunction bipolar transistors with a carbon-doped base grown by a multi-wafer gas-source molecular beam epitaxy (GSMBE) system, which was developed by ourselves. A large-area uniform growth of p-type GaAs and InGaP has been realized. The variation in layer thickness of these layers was less than ± 1.8% across three 3-inch wafers. A large-area (200 × 200 μm 2 ) heterojunction bipolar transistor (HBT) with a base-sheet resistance of 350 Ω showed a high current gain of 190. This is effectively the highest value considering the base sheet resistance, and is comparable to the best data of AlGaAs/GaAs HBTs reported so far. The small signal current gains showed an excellent uniformity of 3% across one of five 2-inch wafers. The wafer-to-wafer variation of current gains for the two 2-inch wafers, in the same growth run, was less than 3%. The base sheet resistances also showed an excellent uniformity of 0.86%. In addition the average base sheet resistances of the two 2-inch wafers was the same. The device also showed an excellent high-frequency characteristics. The cut-off frequency ( f t ) of 61 GHz, and the maximum-oscillation frequency ( f max ) of 94 GHz were obtained for the transistor having a base dopant concentration of 4 × 10 19 cm −3 . These promising results demonstrate the high potential capability of multi-wafer GSMBE for the production of InGaP/GaAs HBTs.

Electron injection effect on formation and decomposition of C–H complexes in C-doped GaAs Base of H+-implanted InGaP/GaAs HBTs

Abstract We observed the current gain and turn-on voltage variations in H+-implanted InGaP/GaAs heterojunction bipolar transistors with carbon-doped bases under high temperature current stresses. The variation occurs in two stages: the first stage is characterized by a current gain increase and a turn-on voltage decrease, and the second by a current gain decrease and a turn-on voltage increase. The first variation is attributed to a decrease of the hole concentration in the base, caused by the formation of C–H complexes in the base. The second variation arises from an increase of the hole concentration in the base, which is brought about by a decomposition of the C–H complexes. Hydrogen in the base is diffused from the H+-implanted region predominantly during the HBT fabrication process. Both the formation and the decomposition of C–H complexes are assisted by current injection. The formation of C–H complexes may be enhanced by the energy transfer from 2 electrons. The decomposition of C–H complexes is dominated by the capturing of single electrons. After the variation, hydrogen do not cause “essential” degradation. Consequently, the HBTs must be finally free from hydrogen.

Microwave power InAlAs/InGaAs double heterojunction bipolar transistors with 1.5 V-low voltage operation

We report the first demonstration of microwave power performance at an extremely low operation voltage (1.5 V) using InAlAs/InGaAs double-heterojunction bipolar transistors (DHBTs). Fabricated InAlAs/InGaAs DHBTs have a step graded collector structure which suppresses the collector-emitter offset voltage V/sub CE,offset/ of I-V characteristics, enabling us to use power devices at a low operation voltage.

Heavily carbon-doped p-type (In)GaAs grown by gas-source molecular beam epitaxy using diiodomethane

Abstract Heavily carbon-doped p-type In x Ga 1− x As (0≤ x 2 I 2 ), triethylindium (TEIn), triethylgallium (TEGa) and AsH 3 . Hole concentrations as high as 2.1 × 10 20 cm −3 were achieved in GaAs at an electrical activation efficiency of 100%. For In x Ga 1− x As, both the hole and the atomic carbon concentrations gradually decreased as the InAs mole fraction, x , increased from 0.41 to 0.49. Hole concentrations of 5.1 × 10 18 and 1.5 × 10 19 cm −3 for x = 0.49 and x = 0.41, respectively, were obtained by a preliminary experiment. After post-growth annealing (500°C, 5 min under As 4 pressure), the hole concentration increased to 6.2 × 10 18 cm −3 for x = 0.49, probably due to the activation of hydrogen-passivated carbon acceptors.

Improved optical properties of low temperature molecular‐beam epitaxially grown AlGaAs by In incorporation

It was found that the optical properties of AlxGa1−xAs (x: 0.1, 0.3) improved with In incorporation at low substrate temperature by molecular‐beam epitaxial growth. The photoluminescence (PL) intensity at 77 K of n‐In0.03(Al0.1Ga0.9)0.97As increased as the substrate temperature was decreased from 590 to 480 °C. The PL intensity at 77 K of n‐Iny(Al0.1Ga0.9)1−yAs grown at 480 °C increases as the In content, y, is increased from 0 to 0.05. For growth at 480 °C, the PL intensity of n‐In0.03(Al0.1Ga0.9)0.97As increased by a factor of 17 and the PL intensity of n‐In0.03(Al0.3Ga0.7)0.97As increased by a factor of 4 compared to those without In, respectively. The improved PL intensity of AlxGa1−xAs (x: 0.1, 0.3) is thought to be from a reduction of group III vacancies by In incorporation, resulting in decreased defect‐related nonradiative recombination.