F. A. Baiocchi

Significant improvement in crystalline quality of molecular beam epitaxially grown GaAs on Si (100) by rapid thermal annealing

Rapid thermal annealing (RTA) has been found to significantly improve the crystalline quality of epitaxial GaAs grown on Si (100) substrates. After RTA at 900 °C for 10 s, the percentage of displaced atoms near the GaAs/Si interface, as estimated by Rutherford backscattering/channeling, decreased from 20 to 7%. Photoluminescence intensity (PL) after RTA increased significantly (as much as sixfold in some cases), with the actual increase varying from sample to sample and with annealing conditions. In some cases, the PL intensity after RTA was comparable to the PL intensity obtained from GaAs grown on GaAs substrate under similar conditions. Rapid thermal annealing at 940 °C resulted in a degradation of the PL intensity as compared to annealing at 900 °C. Also, the PL peaks after RTA were found to shift to lower energies by 2–5 meV at low temperatures.

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.

Damage to InP and InGaAsP surfaces resulting from CH4/H2 reactive ion etching

Structural and electrical damage imparted to InP and In0.72Ga0.28As0.6P0.4 (λg≂1.3 μm) surfaces during CH4/H2 reactive ion etching (RIE) have been examined. X‐ray photoelectron spectroscopy was used to monitor changes in the surface chemistry, Rutherford backscattering spectrometry was used to measure crystallographic damage, and current‐voltage and capacitance‐voltage measurements were made to examine electrically active damage and its depth. Two classes of damage are observed: crystallographic damage originating from preferential loss of P (As) and/or ion bombardment‐induced collision cascade mixing and, for p‐type material, hydrogen passivation of Zn acceptors. Etching at 13.6 MHz, 60–90 mTorr, 10% CH4/H2, and bias voltages of ∼300 V contains gross (≳1%) damage as measured by RBS to within 40 A and electrically active damage to within 200 A of the surface. This is a factor of 3–6 shallower than other RIE processes operated below 10 mT with comparable or higher bias voltages. Acceptor passivation of bot...

Electron impact ionization cross sections of SiF2

Absolute cross sections are measured for electron impact ionization and dissociative ionization of SiF2 from threshold to 200 eV. A fast (3 keV) neutral beam of SiF2 is formed by charge transfer neutralization of SiF+2 with Xe; it is primarily in the ground electronic state with about 10% in the metastable first excited electronic state (a 3B1). The absolute cross section for ionization of the ground state by 70 eV electrons to the parent SiF+2 is 1.38±0.18 A2. Formation of SiF+ is the major process with a cross section at 70 eV of 2.32±0.30 A2. The cross section at 70 eV for formation of the Si fragment ion is 0.48±0.08 A2. Ion pair production contributes a significant fraction of the positively charged fragment ions.

Laser‐assisted metalorganic molecular beam epitaxy of GaAs

We report preliminary studies of the growth of homoepitaxial GaAs by laser‐assisted metalorganic molecular beam epitaxy, using triethylgallium (TEGa) and As4 sources and a 193 nm ArF excimer laser. Laser irradiation results in a high, selective‐area growth rate at temperatures below 450 °C, where pyrolytic growth is very slow. The process is extremely efficient, with roughly unit probability for impinging TEGa molecules sticking and being dissociated by laser radiation to form GaAs. From the strong dependence on laser fluence, the growth enhancement process appears to be pyrolytic in nature (because of transient heating by the pulsed laser) and not photolytic. The cross section for photolysis must be at least ten times lower than the gas‐phase value (9×10−18 cm2). The surface morphology of films grown at 400 °C is rough at threshold fluences (∼0.10 J/cm2), but becomes smooth at higher fluences (∼0.13 J/cm2). These regions with relatively smooth surfaces exhibit enhanced photoluminescence yields compared t...

Absolute cross sections for electron-impact ionization and dissociative ionization of the SiF free radical

Absolute cross sections for electron‐impact ionization of the SiF free radical from threshold to 200 eV are presented for formation of the parent SiF+ ion and the fragment Si+ and F+ ions. A fast beam of SiF is prepared by charge transfer neutralization of an SiF+ beam. The radicals form in the ground electronic state and predominantly in their ground vibrational state, as shown by agreement of the measured ionization threshold with the ionization potential. The absolute cross section for SiF→SiF+ at 70 eV is 3.90±0.32 A2. The ratio of cross sections for formation of Si+ to that for SiF+ at 70 eV is 0.528±0.024; the ratio for formation of F+ to that of SiF+ is 0.060±0.008. The observed threshold energy for Si+ formation indicates the importance of ion pair formation SiF→Si++F−. Breaks in the cross section at 14.3 and 17 eV are assigned as dissociative ionization thresholds.

Study of Ni as a barrier metal in AuSn soldering application for laser chip/submount assembly

The possibility of replacing Pt in the Ti/Pt/Au base and traditionally used metallurgical structure by Ni, while bonding InP laser chip to a submount with AuSn (80% Au) solder, has been investigated. Various Ni‐based metal alloys have been prepared by evaporation. Reflow experiments were conducted in a chamber under forming gas‐controlled ambient. The Ti/Ni/AuSn system provided much longer surface local freezing duration compared to the Ti/Pt/AuSn system. Scanning electron microscopy analysis revealed a smoother surface morphology for the Ti/Ni/AuSn system after the metal refroze. Auger electron spectroscopy depth profiles indicated the formation of a Ni‐Sn‐Au interacted layer. The interaction took place in two steps: the first stage was the dissolution of Ni into the Au‐Sn liquid followed by precipitation of a Ni‐Sn‐Au intermetallic compound; the second stage was a solid‐state interdiffusion of Sn, Au, and Ni which occured in the interacted layer and in the original Ni layer. The latter step was a diffus...

Electron‐impact ionization cross sections of the SiF3 free radical

Absolute cross sections for electron‐impact ionization of the SiF3 free radical from threshold to 200 eV are presented for formation of the parent SiF+3 ion and the fragment SiF+2, SiF+, and Si+ ions. A 3 keV beam of SiF3 is prepared by near‐resonant charge transfer of SiF+3 with 1,3,5‐trimethylbenzene. The beam contains only ground electronic state neutral radicals, but with as much as 1.5 eV of vibrational energy. The absolute cross section for formation of the parent ion at 70 eV is 0.67±0.09 A2. At 70 eV the formation of SiF+2 is the major process, having a cross section 2.51±0.02 times larger than that of the parent ion, while the SiF+ fragment has a cross section 1.47±0.08 times larger than the parent. Threshold measurements show that ion pair dissociation processes make a significant contribution to the formation of positively charged fragment ions.

Tantalum nitride as a diffusion barrier between Pd2Si or CoSi2 and aluminum

Reactively sputtered tantalum nitride (Ta2N) has been investigated as a diffusion barrier between Pd2Si and aluminum and CoSi2 and Al. Ta2N is found to be an excellent matallurgical diffusion barrier for the two systems up to 555 °C, with no intermixing observed in Rutherford backscattering and Auger electron spectroscopic studies. Schottky barrier devices n‐Si/Pd2Si/Ta2N/Al were excellent and showed no deterioration after annealing at 500 °C. However, similar devices with CoSi2 contacts and Ta2N barrier showed a creation of high contact resistance between the silicide and the as‐deposited nitride.

Ti/Pt/AuSn metallization scheme for bonding of InP-based laser diodes to chemical vapor deposited diamond submounts

Abstract A layered structure (consisting of Ti(100 nm)/Pt(200 nm)/Au(500 nm) and Au-Sn (2.5 μm total in multiple alternating layers)) was studied as a bonding scheme for InP-based laser diodes to chemical vapor deposited (CVD) diamond substrates. This structure provided a molten Au-Sn layer of eutectic composition (80:20 wt.%) on top of the Ti/Pt adhesion and barrier metals for about 6 s in the temperature range 300–350 °C and allowed for efficient bonding of the device to the substrate. Longer heating durations allowed a reaction between the Pt and Sn to consume significant amounts of Sn from the solder, thus elevating its melting temperature and resolidifying the solder. With optimum bonding conditions, a high-quality bond of the InP-based laser diode to the CVD diamond substrate was observed, and the electrical performance of the diode was superior to that of diodes that were bonded with the standard In/BeO configurations.