S. J. Pearton

Stability of carbon and beryllium‐doped base GaAs/AlGaAs heterojunction bipolar transistors

GaAs/AlGaAs heterojunction bipolar transitors (HBTs) utilizing highly Be‐doped base layers display a rapid degradation of dc current gain and junction ideality factors during bias application at elevated temperature. For example, the gain of a 2×10 μm2 device with a 4×1019 cm−3 Be‐doped base layer operated at 200 °C with a collector current of 2.5×104 A cm−2 falls from 16 to 1.5 within 2 h. Both the base emitter and base collector junction ideality factors also rise rapidly during device operation, and this current‐induced degradation is consistent with recombination‐enhanced diffusion of Be interstitials producing graded junctions. By sharp contrast, devices with highly C‐doped (p=7×1019 cm−3) base layers operated under the same conditions show no measurable degradation over much longer periods (12 h). This high degree of stability is most likely a result of the fact that C occupies the As sublattice, rather than the Ga sublattice as in the case of Be, and also has a higher solubility than Be. The effect...

High quality AlxGa1−xAs grown by organometallic vapor phase epitaxy using trimethylamine alane as the aluminum precursor

High quality AlxGa1−xAs has been grown by low‐pressure (30 Torr) organometallic vapor phase epitaxy (OMVPE) using a novel precursor, trimethylamine alane (TMAAl), as the aluminum source. The epilayers exhibited featureless surface morphology, very strong room‐temperature photoluminescence (PL), and excellent compositional uniformity (x=0.235±0.002 over a 40 mm diameter). The residual carbon incorporation, which determined the background doping, depended largely upon the choice of gallium precursor. Using triethylgallium, carbon incorporation could be largely suppressed ([C]≪1016 cm−3). The carbon‐related emission intensity was less than the bound exciton emission in low‐temperature (1.6 K) PL even at excitation powers as low as 50 μW cm−2. By sharp contrast, the use of trimethylgallium led to much higher C concentrations (2–5×1017cm−3). Under appropriate conditions, therefore, the use of TMAAl produces extremely high purity AlGaAs of superior quality to AlGaAs grown using conventional precursors.

Electrical and structural changes in the near surface of reactively ion etched InP

Near‐surface (∼1000 A) modification in the net carrier concentration in n‐type InP (n=6×1015–1.5×1017 cm−3) was observed after reactive ion etching (RIE) in Cl‐based (CCl2F2/O2) or organic‐based (C2H6/H2) discharges. The carrier loss is slightly more pronounced in the latter case, due possibly to the creation of deep level, compensating acceptors at greater depths as a result of implantation of the light hydrogen ions. Near‐complete recovery of the initial carrier density occurs after annealing at 500 °C for 30 s. Structural disorder is detected by ion channeling to depths of ∼400 A after C2H6/H2 RIE with a self‐bias of 380 V. This disorder shows significant recovery after 400 °C, 30 s annealing. Current‐voltage measurements on Au Schottky diodes showed ohmic behavior after etching of the InP in a C2H6/H2 discharge, due to the nonstoichiometric surface remaining after RIE. Diodes fabricated on CCl2F2/O2 etched material show only a slight increase in reverse current compared to unetched control samples.

Room‐temperature lasing action in In0.51Ga0.49P/In0.2Ga0.8As microcylinder laser diodes

We report room‐temperature operation of electrically pumped whispering‐gallery mode In0.51Ga0.49P/In0.2Ga0.8As microcylinder laser diodes with emission at wavelength λ=1.0 μm and threshold current Ith=5 mA. Because the lasing modes do not overlap the diode’s central region, carrier density is not efficiently pinned by above‐threshold stimulated emission.

Improved performance of carbon-doped GaAs base heterojunction bipolar transistors through the use of InGaP

Carbon‐doped GaAs/AlGaAs heterojunction bipolar transistors (HBTs) typically exhibit severe leakage at the base‐emitter interface which limits their utility for low‐current applications. Furthermore, the device breakdown voltage, and hence power handling capability, is limited due to the band gap of the GaAs collector material. In this letter we will demonstrate for the first time that both of these limitations can be overcome through the use of InGaP. Since InGaP is not readily doped with carbon, it does not suffer from compensation due to carryover of carbon from the GaAs base. Hence, the ideality factor of the base‐emitter junction improves from 1.3 to 1.09 when the conventional n‐AlGaAs emitter layer is replaced with n‐InGaP. Moreover, InGaP eliminates the crossover of the base and collector currents typically observed in heavily carbon doped GaAs HBTs. This results in the maintenance of gain even at very low collector currents. As a collector material, we have found that InGaP produces significantly ...

HYDROGEN IN CARBON-DOPED GAAS GROWN BY METALORGANIC MOLECULAR BEAM EPITAXY

Atomic profiles show that hydrogen is incorporated in GaAs:C that has been grown by metalorganic molecular beam epitaxy. The hydrogen concentration has been found to be about 5% of the carbon concentration for our growth conditions. An infrared absorption study shows that this hydrogen is involved in stable C‐H complexes. At the lower C concentrations (<1019 cm−3) the CAs‐H complex is the dominant species involving C and H. At higher C concentrations new complexes involving C and H appear.

Passivation of carbon-doped GaAs layers by hydrogen introduced by annealing and growth ambients

Carbon acceptors in GaAs epitaxial layers grown from metalorganic sources are often partially passivated by hydrogen following growth. Here we examine heavily C‐doped GaAs epilayers grown by metalorganic molecular beam epitaxy and metalorganic vapor phase epitaxy by infrared absorption, secondary ion mass spectrometry, and Hall measurements. The concentration of passivated C has been determined by calibrating the intensity of infrared absorption due to C‐H complexes. We have investigated the sources of H in the layers and have found that H2 in the growth and annealing ambients is especially effective in passivating C. A brief anneal in an inert ambient at temperatures above 550 °C is sufficient to activate C acceptors that are passivated by H.

Electron cyclotron resonance plasma etching of InP in CH4/H2/Ar

Plasma etching of InP in a microwave (2.45 GHz) electron cyclotron resonance (ECR) CH4/H2/Ar discharge has been investigated as a function of additional radio frequency (rf, 13.56 MHz) self‐biasing of the sample. The etch rate of InP in a 1 mTorr, 250 W CH4/H2/Ar (5/15/7) ECR discharge increases linearly with applied rf bias, from 50 A min−1 at 0 V to 350 A min−1 at 200 V. Etching under ECR conditions alone yields smooth surface morphologies, while additional rf biasing of the discharge leads to In droplets remaining on the surface. This appears to be a result of preferential removal of P by the high atomic hydrogen density in the discharge. The room‐temperature photoluminescence intensity from InP is reduced by approximately an order of magnitude after ECR etching, but is restored after removal of ∼20 A from the surface by wet chemical etching. Gold Schottky contacts on InP samples etched under ECR conditions only yield barrier heights of 0.48 eV and ideality factors of 1.1, essentially identical to thos...

Properties of titanium nitride thin films deposited by rapid‐thermal‐low‐pressure‐metalorganic‐chemical‐vapor‐deposition technique using tetrakis (dimethylamido) titanium precursor

Titanium nitride (TiNx) thin films were deposited onto InP by means of the rapid‐thermal‐low‐pressure‐chemical‐vapor‐deposition (RT‐LPMOCVD) technique, using the tetrakis (dimethylamido) titanium (Ti(NMe2)4 or DMATi) complex as the precursor. Depositions were successfully carried out at temperatures below 550 °C, pressure range of 5–20 Torr and duration of 50 to 90 s, to give layer thicknesses up to 200 nm and growth rates in the range of 0.8 to 4.5 nm/s. These films had a stoichiometric structure and contained nitrogen and titanium in a ratio close to unity, but also contained a significant amount of carbon and oxygen. The elements were spread uniformly through the films, the nitrogen was Ti bounded, and the carbon was partially titanium bonded and organic bonded as well. The film resistivity was in the range of 400–800 μΩ cm−2; the stress was always compressive, in the range of − 0.5 × 109 to − 2 × 1010 dyne cm−2, and the film had a good morphology. These layers performed as an ohmic contact while depos...

Evidence for the existence of a negatively charged hydrogen species in plasma‐treated n‐type Si

We demonstrate the drift of a donor‐passivating hydrogen species under the action of the electric field in the depletion region of a reverse‐biased Au/n‐Si Schottky diode hydrogenated by exposure to a low‐frequency discharge. The redistribution is explained by the unidirectional drift of a negatively charged passivating species and is confirmed by secondary‐ion mass spectrometry profiling in deuterated diodes. The results are consistent with the presence of an acceptor level for hydrogen in n‐type Si, and are analogous to the situation in p‐type Si where drift experiments reveal the existence of positively charged hydrogen donor species.