Heterojunction Bipolar Phototransistor Research Articles

Planar, Al_03Ga_07As-passivated-base, heterojunction bipolar phototransistors

New planar GaAs heterojunction bipolar phototransistors have been designed and demonstrated. The devices use a GaAs/Al(0.3)Ga(0.7) As molecular-beam-epitaxy materials system with an Al(0.3)Ga(0.7) As passivated, 10-nm-thick base; a depleted, high-low emitter; and a low emitter-base capacitance. Electrical contact to the emitter is made by a set of parallel, ohmic fingers and to the collector by an ohmic contact formed in a large, approximately 1.48-microm deep via. Rise times in response to impulse optical excitation at 810 nm were 747-891 ps except at the two lowest optical excitation powers measured. Photocurrent gains measured at 810 and 850 nm were 0.67-19, depending on experimental conditions. These devices are promising for use in heterodyne photodetector arrays for coherent optical processing channelizers requiring a 100-MHz bandwidth.

Electro-optical mixing in an edge-coupled GaInAs/InPheterojunction phototransistor

Gain nonlinearities at low optical power of an edge coupled GaInAs/InP heterojunction bipolar phototransistor are used to mix the optical demodulation products of two (or more) laser beams. One beam could be CW or low frequency range modulated, since the other one is RF or microwave modulated. Experiments carried out for 2 GHz and 2 kHz, respectively, show the mixing of the two demodulated electrical signals in the phototransistor.

Optical injection locking of microstrip MESFET oscillatorusing heterojunction phototransistors

A heterojunction bipolar phototransistor (HPT) has been used to provide the locking signal to a 2.1 GHz microstrip MESFET oscillator. The oscillator design facilitates the use of the large locking signal provided by the HPT to give relative locking bandwidths (B/f0) of up to 10%, much wider than has yet been reported for an optically injection-locked oscillator.

GaAs/InGaAs/AlGaAs optoelectronic switch in avalanche heterojunction phototransistor vertically integrated with a resonant cavity

An optoelectronic switch with high sensitivity based on avalanche multiplication is demonstrated in a GaAs/InGaAs/AlGaAs heterojunction bipolar phototransistor (HPT) with an integrated resonant cavity. The device, similar to a resonant-cavity enhanced HPT, consists of a four layer n+-p+-i-n structure. Excellent electrical switching characteristics with a high control voltage efficiency (Vs/Vh) of 1.8 have been obtained when the device is operated in the dark. The device can be switched optically at a selected wavelength owing to the integrated resonant cavity. By exploiting the inherent high optical gain, an extremely high optical control sensitivity (∂Vs/∂P0), exceeding 6 V/μW, has been achieved.

Optical-gain enhancement in resonant-cavity heterojunction bipolar phototransistor through emitter-edge thinning

The authors use a lateral emitter resistor in floating base GaAs/InGaAs/AlGaAs heteroj unction bipolar phototransistors to reduce the surface recombination in the vertical wall of the emitter-base junction and increase the photosensitivity at low injection levels. The same process also reduces the dark current in the reverse biased collector junction.

Resonant-cavity InGaAlAs/InGaAs/InAlAs phototransistors with high gain for 1.3–1.6 μm

We describe the characteristics of resonant-cavity heterojunction bipolar phototransistors (RCHPTs) grown on InP substrates. The active layers are part of a Fabry–Perot cavity in which gold is the top reflector and an InGaAlAs/InAlAs quarter-wave stack is the bottom reflector. The stack and active layer thicknesses are such that the absorption is resonantly enhanced by ∼100% at 1.28 μm in one wafer and 1.52 μm in another. An enhancement in photocurrent response also of ∼100% is obtained at resonance. A dc phototransistor current gain of 5000, corresponding to an optical gain of ∼2500 at resonance, was measured on a three-terminal device in a RCHPT wafer.

High-gain InGaAlAs/InGaAs heterojunction bipolar transistors and phototransistors

The characteristics of InGaAlAs/InGaAs heterojunction bipolar transistors (HBTs) grown by molecular beam epitaxy are described. A current gain of 15600 at a current density of approximately 10/sup 4/ A/cm/sup 2/ and an emitter-base heterojunction ideality factor of 1.02 were measured. Appropriately designed InGaAlAs/InGaAs HBTs, when operated as phototransistors, also had high gains. A current gain of 1000 for a collector current of only 10 mu A was obtained for phototransistors. Such high gains are due to low recombination currents as a consequence of the good crystalline quality of the InGaAlAs bulk and InGaAlAs/InGaAs interface.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

High-gain resonant InGaAlAs/InGaAs heterojunction bipolar phototransistors grown by molecular beam epitaxy

Summary form only given. Results obtained with two approaches that significantly enhance the gain and sensitivity of InP-based heterojunction phototransistors (HPTs) grown by molecular beam epitaxy (MBE) are described. The use of quaternary InGaAlAs (300 K, E/sub g/ approximately 1.08 eV) as the high-bandgap emitter layer improves the quality of the emitter-base interface and leads to high current gains, even at very low current levels. For heterojunction bipolar transistors (HBTs) with a circular (50- mu m diameter) emitter, DC current gains of more than 9000 were obtained at a current density of 1000 A/cm/sup 2/. In the second approach to enhancing the gain and sensitivity of HPTs while keeping the absorbing layer thickness the same, a resonant structure in which the active layers are part of a Fabry-Perot cavity with the end reflectors being gold (which also serves as the emitter contact) and an InAlAs/InGaAlAs quarter-wave stack was designed. >

Gain and frequency response of a graded-base heterojunction bipolar phototransistor

A study has been made of the carrier transport and optical gain of a heterojunction bipolar phototransistor in the presence of a drift field in the base region. The computational method employed is based on transfer matrices for minority-carrier density in the base region in the presence of ionizing radiation. Scattering matrices for the electron and hole currents are used for computing the avalanche multiplication in the collector junction. The effect of varying the ratio of absorption in the base region to that in the collector has been examined. The expressions derived have been used to estimate the frequency response of the bipolar heterojunction phototransistor.

High current gain heterojunction bipolar phototransistor for monolithic integrated photoreceiver

The first monolithic photoreceiver integrating an HPT, two HBT's on a GaAs chip has been designed, fabricated and tested. A sensitivity of -30 dBM for 140 Mbit/s transmission rate was inferred from signal to noise ratio measurement. Taking into account the specific characteristics of high current gain-high speed heterojunction phototransistor, the receiver sensitivity has been analysed. For high current gain HPT's, the base layer is very thin and in this case, the early effect and the thermal noise of the base access resistance have to be taken into account. This leads to a trade-off between the base resistance and the current gain. Compared to PIN-FET receivers, the range of interest for HPT, from the point of view of sensitivity is located above a few hundreds Mbit/s, but for a monolithic photoreceiver implemented with HPT and heterojunction bipolar transisitors (HBT's) and advantages of monolithic integration leads to an extension of the application range.

GaAs/GaAlAs Heterojunction Bipolar Phototransistor for Monolithic Photoreceiver Operating at 140 Mbit/s

The development of optical transmission calls for sensitive and fast optoelectic transducers. With the advent of optical local area networks, hybrid transducers may no longer be appropriate, and monolithic emitters and receivers will be preferred. In this paper, we report on the first monolithic photoreceiver implemented with GaAs-GaAIAs bipolar devices. One phototransistor and two transistors are integrated, together with four resistors on a 0.5x0.5-mm/sup 2/ GaAs chip. The transimpedance receiver has a bandwidth of 80 MHz. SignaI and noise power measurements indicate that for a digital signal at 140 Mbit/s, the minimum detectable power is 1 µW (-30 dBm).

Monolithic integrated photoreceiver implemented with GaAs/GaAlAs heterojunction bipolar phototransistor and transistors

The first monolithic integrated photodetector-preamplifier implemented with GaAs/GaAlAs heterojunction phototransistor and transistors has been fabricated and tested. This photoreceiver has been designed for local networks of optical transmission links operating at 0.85 ?m wavelength with multimode fibres. A heterojunction phototransistor (HPT), two heterojunction bipolar transistors (HBTs) and four resistors are integrated in a 0.5 × 0.5 mm2 GaAs chip. The photoreceiver with a 26 k? external feedback resistor has a bandwidth of 80 MHz with a transimpedance gain of 7000 V/A. The noise measurements indicate that a minimum detectable power of ?30 dBm is obtained at 140 Mbit/s for an error rate of 10?9.

Monolithic integrated photoreceiver implemented with Ga 1−xAl x As/GaAs heterojunction bipolar phototransistor

We have optimized the growth conditions of (Ga,Al)As/GaAs heterojunction bipolar phototransistors (HPT's) using MOCVD or MBE techniques. Devices with current-gains higher than 3000 and low input capacitances have been obtained using a fabrication process suitable for IC's. A photoreceiver has been designed with predicted performances of -39.5 dBm at 140 Mbits/s.

Gain of a heterojunction bipolar phototransistor

Analytical expressions have been derived for the collector current, optical gain, and quantum efficiency for a heterojunction, bi-polar phototransistor (HPT). These expressions can be utilized to optimize the current gain and quantum efficiency for HPT design. The presence of avalanche multiplication in the base-collector junction has been taken into account and shown to be a significant factor in determining the gain of an InGaAs/InP phototransistor. Experimental results of optical gain versus the collector-emitter voltage can only be explained in terms Of avalanche multiplication.

GaAlAs/GaAs heterojunction bipolar phototransistors grown by LPE with a current gain of 50 000

A simple mesa GaAlAs/GaAs heterojunction bipolar phototransistor fabricated by LPE growth technique is presented. A high current gain of the order of 50 000 has been obtained and is believed to be the highest ever reported for a bipolar device. The corresponding high sensitivity is about 15 000 A/W for an 800 nm illumination wavelength.

High-speed GaAs heterojunction bipolar phototransistor grown by molecular beam epitaxy

A novel heterojunction phototransistor (HPT) structure is proposed using two base regions such that the emitter-base depletion region is located in the wide-gap material. Very small area HPTs have been fabricated on semi-insulating substrates. Maximum current gain is β = 300. The response time, with rise time as short as 250 ps and FWHM = 320 ps, has been obtained using a picosecond pulse dye laser.