K. Z. Zhang

An inquiry concerning the principles of Si 2p core‐level photoemission shift assignments at the Si/SiO2 interface

It has long been held that high resolution x‐ray photoemission spectra of the Si 2p core level at SiSiO2 interfaces provide important structural information, and that any credible interfacial model must be able to account for these data. To this end it has traditionally been assumed that there existed a one‐to‐one relationship between chemically shifted spectral features and interfacial silicon atoms in specific formal oxidation states. A series of new measurements of Si 2p core level binding energies for cluster‐derived Si/Si oxide interfaces appear to stand in direct contradiction to this critical assumption. In this article we present a critique of various responses to the challenge posed by the new observations. Particular attention is given to the logical consequences of either maintaining or rejecting the one‐to‐one relationship between shifted features and formal silicon oxidation states and to the challenges each of these responses must meet if they are to prevail.

THE ROLE OF SECOND-NEIGHBOR EFFECTS IN PHOTOEMISSION : ARE SILICON SURFACES AND INTERFACES SPECIAL?

A widely used assignment scheme for Si 2p core-level photoemission studies of silicon oxidation relies solely on the formal oxidation state of the silicon. The tacit assumption of this assignment methodology is that second-neighbor effects have no measurable effect on observed Si 2p binding energies. In this letter, new experiments are combined with literature precedents to make the case that the second-neighbor effects play an important role in determining binding energy shifts.

Self-limiting chemical vapor deposition of an ultra-thin silicon oxide film using tri-(tert-butoxy)silanol

Abstract Tri-( tert -butoxy)silanol (tBOS) rapidly forms a self-limited ∼10-A-thick silicon oxide film upon exposure to a Si(100)-2×1 surface at 300 K. The majority of hydrocarbon spontaneously desorbs at this temperature. Heating to ∼700 K removes the remaining tert -butoxy groups. The films were characterized by conventional X-ray photoelectron spectroscopy (XPS), synchrotron XPS of the Si 2p core-level and valence band regions, and reflection absorption infrared spectroscopy (RAIRS).

RECOMBINATION CHARACTERISTICS OF MINORITY CARRIERS NEAR THE ALXOY/GAAS INTERFACE USING THE LIGHT BEAM INDUCED CURRENT TECHNIQUE

The light beam induced current (LBIC) technique was used to characterize the interface formed by the wet oxidation of AlAs and AlxGa1−xAs (x=0.98 and 0.95). LBIC scans were used to calculate the diffusion lengths of minority carriers both in the bulk and near these interfaces; and the corresponding interface recombination velocities were estimated. The interface recombination velocity at the oxide/semiconductor interface is 3.13×105u2009cm/s for AlAs, and 1.90×104u2009cm/s for Al0.98Ga0.02As. It is found that the addition of gallium in the AlAs can significantly improve this property.

Reduction of Be out‐diffusion from heavily doped GaAs:Be layers by pseudomorphic InxGa1−xAs barrier layers

The effectiveness of suppressing Be out‐diffusion from a Be‐doped GaAs layer by strained InGaAs layers using secondary ion mass spectroscopy has been evaluated. The experimental structures consist of an 800 A Be‐doped (∼1×1019 cm−3) GaAs layer sandwiched between 80 A InxGa1−xAs (x=0,0.1,0.25) layers. The samples were subjected to rapid thermal annealing (RTA) at 750u2009°C for 6 min. It is clearly observed that Be diffusion beyond the InGaAs layers is the fastest for the structure with x=0 and the slowest for the structure with x=0.25.

Reflection–absorption infrared investigation of hydrogenated silicon oxide generated by the thermal decomposition of H8Si8O12 clusters

Reflection–absorption infrared spectroscopy has been employed to observe Si–H bonds within a model, ultrathin silicon oxide. Upon heating a monolayer of H8Si8O12/Si(100−2×1 to 700u2009°C, Si–H bonds as a part of HSiO3 entities are still detected within the oxide layer after cooling. These fragments appear to be stable to temperatures of at least 850u2009°C. Reversible hydrogen/deuterium exchange for these entities is also directly observed.

Reliability of strained quantum well lasers

Strained quantum well lasers have demonstrated remarkably improved characteristics compared to unstrained quantum well lasers. For extracting the highest level of performance, the required strain may be large. An important factor in the use of strained quantum wells is the long-term stability of the pseudomorphic active region and the associated reliability of the device. The effect of strain on reliability is investigated, in particular, for In/sub x/Ga/sub 1-x/As/GaAs (x=0.2, 0.25, and 0.3) multiple quantum well lasers in 64 mW/facet constant output power tests at 85/spl deg/C for 40 hours. Laser characteristics such as the operating currents (I/sub op/), the threshold currents (I/sub th/), and the slope efficiencies (dL/dI) are measured during the test and serve as useful degradation parameters. The average changes in I/sub op/ are 15, 9.9, and 0.22%, and the average changes in I/sub th/ at 85/spl deg/C are 21, 8.7, and -1.2% for x=0.2, 0.25, and 0.3, respectively. The average changes in dL/dI at 85/spl deg/C are -19, -14, 1.5%, respectively. Defect migration into the pseudomorphic active region is verified to be the dominant mechanism of degradation observed in these lasers. Hence, to account for the strain-induced reliability improvement, it is necessary to study the propagation of defects in semiconductor heterostructures. A theoretical model is constructed based on the the linear theory of elasticity, and relevant experiments are conducted for its support. Strain energy considerations show that defect propagation across a strained layer is unfavorable. The nonradiative defect densities in the GaAs-Al/sub 0.4/Ga/sub 0.6/As quantum wells with and without the surrounding pseudomorphic In/sub 0.2/Ga/sub 0.8/As layers are compared by measuring the photoluminescence intensities after intentionally creating defects and enhancing their diffusion. The structures with pseudomorphic In/sub 0.2/Ga/sub 0.8/As layers consistently show much higher quantum well photoluminescence intensity by as much as 130 times, thereby confirming our model. These results clearly account for the observed reliability improvement in quantum well lasers with increased strain in the well.<<ETX>>