S. Neumann

Surface recombination mechanism in graded-base InGaAs-InP HBTs

The surface recombination at extrinsic base region in graded-base InGaAs-InP heterostructure bipolar transistors (HBTs) is studied. The (NH/sub 4/)/sub 2/S treatment eliminates the surface recombination, seen from the size-independent current gain. The surface recombination currents of the selfand nonself-aligned HBTs have different behavior. The mechanism of it is discussed.

Photoluminescence of GaAs nanowhiskers grown on Si substrate

GaAs nanowhiskers were grown by metalorganic vapor-phase epitaxy on (111) Si substrates using the vapor-liquid-solid growth mode. The diameter of the nanowhiskers was defined by polydisperse catalytic Au nanoparticles in the range from 5 to 100 nm deposited on the Si substrate from the liquid phase. The low-temperature photoluminescence spectra exhibit a series of unresolved exciton-related transitions shifted to a shorter wavelength due to the quantization effects. Despite some structure defects, relatively high photoluminescence intensity and its linear dependence on the excitation power without saturation confirms the good material quality of fabricated GaAs nanowhiskers.

Current transport mechanisms and their effects on the performances of InP-based double heterojunction bipolar transistors with different base structures

InP-based double heterojunction bipolar transistors (DHBTs) with different base structures were studied. The base structures are InGaAs with and without graded composition and GaAsSb. Both of the terminal currents of InP/GaAsSb/InP DHBT in forward and reverse modes are limited by the carrier transport across the base layer. This causes the offset voltage to be determined by the difference between the base-collector and base-emitter areas and by the normal common-base current gain. The emitter currents of both graded- and abrupt-base InP/InGaAs/InP DHBTs in the reverse mode are also limited by the carrier transport across the base layer, while their collector currents are limited by the band discontinuity of the base–emitter junction. The different current transport mechanisms of the terminal currents in the forward and reverse modes result in the larger offset voltage.

Comparison of the passivation effects on self- and non-self-aligned InP/InGaAs/InP double heterostructure bipolar transistors by low-temperature deposited SiNx

Both the self- and non-self-aligned graded-base InP/InGaAs/InP double heterostructure bipolar transistors (DHBTs) were passivated by room-temperature deposited SiNx. Current gains were found to increase significantly after SiNx passivation. The passivation resulted in an increase in the leakage current of base-collector junction. The larger leakage current in the non-self-aligned DHBT made the sudden increase of the collector current in the common-emitter I–V curve occur at smaller collector-emitter bias than that in the self-aligned DHBT, which has smaller leakage current. Further increase in the current gain was found after the DHBTs were exposed to air for 200 days. The leakage current in the base-collector diode was reduced. The sudden increase of the collector current in the non-self-aligned DHBT in the common-emitter I–V characteristics was also suppressed. Investigation of reverse Gummel plots showed that the surface recombination in the base-collector diode was suppressed by the passivation. The l...

Integration of heterostructure bipolar transistor and electroabsorption waveguide modulator based on a multifunctional layer design for 1.55 /spl mu/m

An electroabsorption waveguide modulator (EAM) for 1.55 /spl mu/m is embedded into the layer-stack of a heterostructure bipolar transistor (HBT). The collector consists of a complete optical waveguide and enables the monolithic integration of modulators, transistors and also a new merged device to result in a modulator with integrated amplifier. At present this device offers a 3 dB cut-off frequency for optical modulation of 7 GHz and for pure electrical operation cut-off frequencies of f/sub T/ and f/sub max/ both of about 25 GHz.

Sulfur and low-temperature SiNx passivation of self-aligned graded-base InGaAs/InP heterostructure bipolar transistors

The passivation of self-aligned InGaAs/InP heterostructure bipolar transistors (HBTs) with graded base by the combination of S and low-temperature deposited SiN, was investigated. Base current was found to decrease after the passivation. Collector current significantly increases at low base-emitter voltages. The increase is attributed to the leakage current of the base-collector diode. The current gain was found to increase. When annealing was performed at 300 degreesC for 5 min, the base current decreases further and the collector currentdecreases. The leakage of collector current was found to be suppressed. The current gain was further improved and the leakage current can affect the Gummel plots. The leakage source was identified to be the interface between the semiconductor and the SiN, layer. The leakage current can be decreased by the annealing process.

Characterisation of GaAs nanowhiskers grown on GaAs and Si substrates

We report the growth of GaAs nanowhiskers on GaAs and Si substrates using two alternative Ga-precursors and demonstrate results of photoluminescence and electrical characterisation of the grown structures towards the fabrication of III/V nanoscaled optoelectronic devices on Si substrate.

Design and modelling of a III/V mobile-gate with optical input on a silicon substrate

The co-integration of III/V devices such as InGaAsP PIN diode and an (In)AlAs/In(Ga)As Resonant Tunnelling Diodes with state-of-the-art silicon NMOS transistors is studied. The III/V devices layers are epitaxially grown and fabricated on silicon substrates for the extraction of model parameters. The performance of a potentially low-cost optical receiver circuit on silicon is simulated using HSPICE up to 10 Gb/s.

Growth of carbon-doped LP-MOVPE InAlAs using non-gaseous sources

Carbon-doped InAlAs grown by LP-MOVPE lattice matched on InP is investigated at various growth temperatures. The liquid source tertiarybutylarsin instead of arsine is used to realize a high layer quality at reduced growth temperature and a low V/III ratio. Carbon tetrabromide serves as carbon doping source providing a high doping level and a small diffusion. A p-type doping is achieved at a growth temperature of 540°C and below. The p-type doping concentration is proportional to the adjusted carbon tetrabromide flow rate. A doping concentration of electrically activated acceptors of up to p = 1 x 10 20 cm -3 is achieved at a growth temperature of 520°C.

Buffer optimization for InP-on-Si [001] quasi-substrates

Different types of InGaAs/InP(InAlAs) superlattice structures and low temperature grown single InAlAs layers are examined with respect to the defect reduction and improvement of the surface roughness of InP-on-Si [001] quasi-substrates. By using an InAlAs layer grown at optimized conditions a surface roughness of 1.9 nm and a good crystal quality are achieved. Resonant-tunneling diodes fabricated on top of the improved quasi-substrate exhibit a peak-to-valley-ratio of 2 and a peak current density of 27 kA/cm at room temperature showing the high application potential of this approach.