We report the results of experiments during which epitaxially grown n-GaAs was exposed to He- and SiCl4-plasmas at similar sets of well defined RF powers and plasma pressures. To study the defects introduced during these plasma exposured, we employed deep level transient spectroscopy (DLTS). The effect of the plasma etch induced defects on the performance of Schottky barrier diodes (SBDs) fabricated on plasma processed GaAs was evaluated by current-voltage (IV) and capacitance-voltage (CV) measurements. DLTS revealed that each plasma type (He and SiCl4) introduced its own characteristic set of defects. Some of the defects created during He processing and one defect introduced by SiCl4 etching had identical electronic properties to those introduced during high energy (MeV) He ion bombardment. SiC14etching introduced only two prominent defects, one of which is metastable with electronic properties similar to a metastable defect previously reported in high and low energy He-ion bombardment of Si-doped GaAs. IV measurements demonstrated that the characteristics of SBDs fabricated on He-ion processed surfaces were very poor compared to those of control diodes (diodes fabricated on surfaces cleaned by conventional wet etching). In contrast, the properties of SBDs fabricated on SiCl4 etched surfaces were as good as, and in some cases superior to, those of control diodes. SBDs fabricated on annealed (at 450°C for 30 minutes) He-processed samples exhibited improved but still poor rectification. In contrast, SBDs fabricated on annealed SiCl4 etched surfaces had virtually the same characteristics as those fabricated on unannealed SiCl4 etched samples.

We provide a high throughput method of performing optical modulation spectroscopy, such as photoreflectance or other spectroscopy techniques which include photoluminescence on a micrometric resolution scale of the order of 10 μm. The spectroscopic technique is designed for strain induced by process in silicon wafers. The optical system is optimized using a polarizing beamsplitter in conjunction with a single Fresnel rhomb for the provision of an optimum separation of the reflected probe beam with minimal optical losses. In addition, a rapid detection system is used that allows the spectrum to be acquired within few seconds.

We present an improved photoreflectance (PR) spectroscopy technique upon the prior art in providing a rapid acquisition method of the PR spectrum in a simultaneous and multiplexed manner. Rapid PR (RPR) application is the on-line monitoring of strained silicon. Shrinkage in the silicon bandgap is measured and converted to strain, using theoretical models. Experimental RPR results are in good correlation with Raman spectroscopy.

In this paper, technological advances of modulation spectroscopy are presented, exploiting the sensitivity, room-temperature resolution, as well as the rapid and non-contact (non-destructive) nature of laser-induced photoreflectance (PR). A novel method of asynchronous (switching) modulation is presented to overcome laser-induced non-PR background effects, which limit or even obscure the complex (phase) PR response. The solid-state, acousto-optic based method may even be employed for non-uniform samples, and moreover, exhibits evidence for improved signal-to-noise level. Also presented is a novel optical design in order to achieve multiple, independent and simultaneous spectral acquisition, including auto-calibration. Results are demonstrated for heavily doped n-type and p-type GaAs substrates, and also technologically important HBT device structures, with further applications also emphasised for HEMTs, LEDs, etc. The results demonstrate the importance and role of PR as a successful commercial metrology tool for existing state-of-art, as well as next generation semiconductor characterisation and statistical-process-control (SPC) equipment.

Advances in the application of non‐contact photoreflectance (PR) spectroscopy to the characterisation of epiwafer device materials are presented. The study examines both vertical cavity surface emitting laser (VCSEL) and heterojunction bipolar transistor (HBTs) device structures. Emphasis is placed on the technologically important applications of VCSEL device material characterisation, for which PR offers the only true non‐destructive testing capability, as well as upon the measurement of electric fields in device epiwafers for rf application transistors such as HBTs. This paper demonstrates the application of non‐destructive and rapid techniques for evaluation and control of compound semiconductor materials for both VCSEL and HBT technology. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

This paper summarises the application of the laser-based electro-absorptive technique of photoreflectance (PR) for the study of vertical cavity surface emitting lasers (VCSELs). PR results are shown to reveal the technologically important cavity mode and ground state quantum well exciton structures. AlGaAs/GaAs based quantum well VCSELs were examined with and without top mirror layers as a function of laser pump excitation conditions, with results compared with angle-dependent PR data. Cavity mode and quantum well alignments were also studied with reference to the un-modulated reflectance signal as well as correlated with photoluminescence data. The results demonstrate the importance of PR metrology for state-of-art VCSEL characterisation.

In this work we report the application of optical spectroscopic techniques namely photoreflectance (PR), ellipsometry and photoluminescence (PL) for qualification of InGaP/GaAs multi-layer heterojunction bipolar transistor (HBT) material. These techniques reveal important information regarding the quality of the different InGaP and GaAs layers for the emitter, base, collector and surface cap regions. In particular PR studies of non-optimal HBT material reveals InGaP (emitter) layer sub-lattice ordering effects, as correlated with selective area electron diffraction patterns (<311> <511>). Moreover, comparison of the emitter/base interface field levels and InGaP ordering data reveals further evidence of a non-abrupt InGaP/GaAs heterojunction, proving to have adverse consequences for HBT current gain characteristics and consistent with measured reduced common emitter current gain. Supporting evidence for such non-optimal, strained emitter/base region is provided from x-ray (004) & (002) diffraction but mainly from cleaved edge (g=002) dark field TEM, revealing significant interfacial non-uniformity, also likely correlated to the emitter layer ordering present. PR spectral information is compared with PL lineshape data - including Arrhenius (thermal) plots, while extracted interfacial electric field data are also supported by device finite-element (ANSYS) modelling. In summary this paper demonstrates the application of non-destructive and rapid techniques for evaluation and control of compound semiconductor materials for HBT technology.

Defects in the emitter region of Ga0.51In0.49P/GaAs heterojunction bipolar transistors (HBTs) were investigated by means of deep-level transient spectroscopy. Both annealed (635 °C, 5 min) and as grown metalorganic chemical vapor deposition epitaxial wafers were investigated in this study, with an electron trap observed in the HBT emitter space-charge region from both wafers. The deep-level activation energy was determined to be 0.87±0.05 eV below the conduction band, the capture cross section 3×10−14 cm2 and the defect density of the order of 1014 cm−3. This defect was also found to be localized at the emitter–base interface.

In this work we have examined the effect of RF annealing (450–750°C, 5–30 min) upon both InGaP/GaAs-based hetero-junction bipolar transistor (HBT) structures, fabricated by metalorganic vapour phase epitaxy (MOVPE), as well as thick carbon (C)-doped p+GaAs HBT base layers with varying layer thickness, dopant level and type (intrinsic and extrinsic C precursors) and co-doping (In) strain compensation. Anneal-induced changes in the p+GaAs layer lattice strain, Hall carrier concentration and mobility were compared with non-radiative losses, determined from photoluminescence (PL) intensity data. Majority and minority carrier property differences were also compared with IR reflection, Raman backscattering and photoreflectance (PR) data and correlated with changes in MOVPE hydrogen background concentration as determined by secondary-ion-mass-spectroscopy (SIMS). Thick base layer (1.3 μm) HBT structures were also examined for different anneal temperatures and time, showing significant changes in the PR emitter(InGaP)/base (p+GaAs) and base/collector (n-GaAs) interface regions for the 650°C anneal condition, as correlated with both PL and SIMS hydrogen concentration data.

Characterisation of UHV-CVD (ultra high vacuum chemical vapour deposition) grown Si/SiGe heterostructure field-effect transistor (HFET) material with a buried, strained silicon layer has been carried out using non-destructive optical techniques. The effect of thermal budget on the heterostructure was investigated by annealing samples at temperatures up to 900°C for 5 min and carrying out analysis using Raman back-scattering spectroscopy. An investigation of silicon cap loss due to native oxide removal etches was carried out using phase-modulated variable angle spectroscopic ellipsometry (VASE) and correlated with Rutherford back-scattering spectroscopy (RBS) measurements.

In this study, optical and structural properties of InGaP/GaAs epitaxial heterostructures are investigated as a function of growth temperature and substrate orientation (2 and 10°). Both ordered and disordered InGaP layers were grown by metal organic vapour phase epitaxy (MOVPE). The complex refractive index both above and below the fundamental band gap has been determined using spectroscopic ellipsometry (SE). In particular an InGaP/GaAs intermixing layer, in addition to the InGaP oxide overlayer was identified and introduced in order to improve the accuracy of the extracted refractive index. Variations in Raman TOm mode and photoluminescence (PL) emission efficiencies show different degrees of ordering, which are correlated to different PL peak energies or bandgaps extracted from SE data. Misfit strain and lattice mismatch are also investigated.

In this work we investigate the optical and band structure properties of full InGaP/GaAs based heterojunction bipolar transistor (HBT) epitaxial structures grown by metalorganic chemical vapour phase epitaxy (MOVPE). In related work, full HBTs have been fabricated from the two wafers studied, which exhibit high and low common-emitter current gain (hFE) parameters on electrical test. The focus of this study is to investigate and compare the photoluminescence and photoreflectance spectroscopy response of these known good and bad epitaxial wafers. The results of low temperature (10–300 K) spectral and transient photoluminescence (PL) analysis are presented, revealing evidence of the nature of the InGaP ordering induced non-radiative loss mechanism. The results also demonstrate the modification to the PL lineshape arising from the InGaP/GaAs interfacial conditions. The experimental results are supported by X-ray diffraction data and finite-element device simulation, showing the effect of intermixing layers on the interfacial band potentials. The optical modulation technique of photoreflectance (PR) spectroscopy was employed to investigate the band structure and interfacial electric fields, Fs, of the HBT structures. Following the polarisation–[110] and [11̄0]–dependence of the sub-lattice ordering PR response, it was found necessary to include an emitter/base intermixing layer in order to account for the InGaP/GaAs Fs data. It is concluded that non-optimal MOVPE growth conditions for one of the structures resulted in both sub-lattice ordering and layer intermixing effects, consistent with the low hFE of the HBTs fabricated from this material.

In this work we have characterised InGaP/GaAs based heterojunction bipolar transistor (HBT) structures, fabricated by metalorganic chemical vapour phase epitaxy (MOVPE), using non-contact electro-optic spectroscopic techniques, photoreflectance (PR), photoluminescence (PL) and ellipsometry. PR analysis details both band structure and interfacial electric field data for both the GaAs collector and InGaP emitter regions. Including sub-lattice ordering for the InGaP alloy, the PR analysis also indicates the presence of an interfacial or intermixing layer between the emitter and GaAs base as a result of non-optimal MOVPE growth. The results are compared with room temperature PL spectra, demonstrating in particular the modification to the PL lineshape arising from the InGaP/GaAs interfacial conditions. The experimental data are also supported with finite-element device simulation, showing the effect of mixing layers on the interfacial band potentials. To interpret the experimental HBT ellipsometric response it was found necessary to include InGaP/GaAs layer intermixing within the optical model, consistent with the previous data. The implications of these results for HBT device performance are also discussed.

Electrochemical sulfidation of n-type GaAs (100) has been investigated under anodic conditions with a view to surface passivation for improved electronic and optical properties. This treatment has successfully removed the native oxide and formed a thick layer of gallium and arsenic sulfides displaying high durability against oxidation and optical degradation compared to conventional dipping treatment using (NH 4 ) 2 S solution. X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), secondary ion mass spectroscopy (SIMS) and atomic force microscopy (AFM) have been used to characterize the treated surfaces. These studies have been used to devise a structural model of the near-surface region. The results of Raman backscattering spectroscopy measurements indicate that there is a 35% reduction of the surface barrier height compared to the untreated surface. This passivation technique has been shown to be effective in reducing surface band bending on GaAs (100) and enhancing the chemical stability of the surface, making it more suitable for electronic and optoelectronic device applications.

We employed capacitance-voltage (C–V) measurements to determine the free-carrier concentration changes in n-GaAs after processing it in a He plasma, and deep-level transient spectroscopy (DLTS) to study the electrical properties of the plasma-induced defects. C–V measurements indicated that He-plasma processing resulted in a strong carrier reduction up to 1 μm below the GaAs surface. DLTS showed that He-ion processing introduced several prominent defects, including the frequently studied radiation-induced defects E1 and E2, associated with VAs. Current-voltage measurements demonstrated that the He-plasma processing inhibits the fabrication of high barrier Schottky diodes on n-GaAs.

We employed deep-level transient spectroscopy to determine the electrical properties of defects introduced in epitaxially grown n-GaAs during dry etching in a SiCl4 plasma at different rf powers and plasma pressures. We found that SiCl4 etching introduced two prominent defects, one of which is metastable. Current–voltage measurements demonstrated that high barrier Schottky barrier diodes can be fabricated on SiCl4-etched n-GaAs surfaces for all power and plasma pressure conditions investigated. The defect concentration decreased and the diode quality improved when etching at lower rf power and higher plasma pressure.

Etching with Ar+ ions and SiCl4 reactive ion etching (RIE) of p type 2-3 Omega cm resistivity Si (100) substrates was characterised using photoreflectance (PR), Rutherford backscattering spectrometry, and spectroscopic ellipsometry. Isochronal (5 min) etching was performed at various de etch biases (0-500 V). ii distinct modification to the Lambda(3)-Lambda(1) Si transition of the room temperature PR spectra was observed as a function of etch bias for both etching modes. It was found that the PR response is sensitive to both the degree and nature of the ion bombardment. (C) 1997 The Institute of Materials.