Gert Paulsson

Accrual Accounting in the Public Sector: Experiences From the Central Government in Sweden

Introduction of accrual accounting is an important component in the New Public (Financial) Management reform movement that has been sweeping over many western countries during the last decades (Olsson et al., 1998). Several studies show that the trend towards accrual accounting is likely to continue during the years to come (OECD, 2000; and Luder and Jones, 2003b). Furthermore, international organisations like the International Federation of Accountants Public Sector Committee (IFAC PSC) and the OECD Public Management Committee (PUMA) directly or indirectly support such a move. For example, IFAC PSC has used the International Accounting Standards (IAS), which are developed for private companies, as a basis for the development of their International Public Sector Accounting Standards (IPSAS). They argue in the following way for this choice:

Optical detection of growth oscillations in high vacuum metalorganic vapor phase epitaxy

We report the first measurements of growth oscillations in high vacuum metalorganic vapor phase epitaxy (MOVPE). The reflection difference response of the surface is used for real‐time monitoring of the layer‐by‐layer growth of GaAs from triethylgallium (TEG) and arsine. The frequency of the optically detected growth oscillations is found to be proportional to the flux of TEG and to the growth rate. We expect our results to extend the more limited ranges of applicability offered by reflection high‐energy electron diffraction to allow the study of growth oscillations also in other MOVPE‐related growth techniques.

Reflectance-difference study of surface chemistry in MOVPE growth

With the advent of the reflectance-difference (RD) technique the electronic configurations of III–V surfaces can be probed also under the non-ultra-high vacuum (UHV) conditions prevailing during metalorganic vapour phase epitaxy (MOVPE). In this paper the surface chemistry involved in the MOVPE growth of GaAs from triethylgallium and arsine is studied in a growth system where the pressure can be changed from high-vacuum (10-3 Torr) to low-pressure (1 Torr) conditions. Studies of the GaAs surface during its exposure to triethylgallium and to arsine are presented. Growth oscillations detected in real time are used to characterize growth and to investigate three-dimensional island formation during Ga saturation. Finally, growth oscillations are used to study the kinetics of the regeneration of ideal, As-terminated, surface conditions.

Reflectance-difference detection of growth oscillations

We have observed damped oscillations measured by the reflectance-difference (RD) technique during growth of GaAs by vacuum chemical epitaxy (VCE) using triethylgallium (TEG) and arsine as precursors. The variation in growth rate with incident TEG flux (at 550°C) was found to be linear for growth rates between 0.1 and 0.4 monolayers/s. Our small, compact RD set-up measures, at nearly normal incidence, the difference between the reflectance of light polarized parallel to the [110] direction and parallel to the [110] direction. This gives information on the lower-symmetry surface since the bulk contribution nominally disappears due to the subtraction. Clearly resolved growth oscillations, having an amplitude of up to one fourth of the initial transient, can be obtained during one single time base scan. After arsine stabilization the RD can follow, in real time, the formation of up to 25 single monolayers, each one corresponding to one period of the growth oscillations. Our results prove that RD can be used during continuous growth providing excellent control of the growing GaAs surface.

Reflectance-difference probing of surface kinetics of (001) GaAs during vacuum chemical epitaxy

Abstract A reflectance-difference (RD) study of the kinetics of various surface processes involved in the growth of GaAs from triethylgallium and arsine is presented. During triethylgallium exposure of an As-stabilized (001) GaAs surface, an initial linear RD response is observed, similar to what has previously been reported for trimethylgallium. We show that in the case of triethylgallium an over-saturation of the surface occurs, which results in complex transients in the RD response and, for a critical dose, in a loss of the surface coherency as determined by the disappearance of RD growth oscillations. It is found that the arsine reactivity on the over-saturated surface is much higher that that on the Ga-stabilized surface. The arsine-induced RD transient is compared with the kinetics of the re-establishment of a perfect As-stabilized surface, using the amplitude of RD-detected growth oscillations as a probe of the status of the surface.

Reflectance difference for in situ control of surface V/III ratio during epitaxial growth of GaAs

Optical, in situ, real time control of surface processes during epitaxy is becoming increasingly important for the understanding and control of crystal growth. Here results are presented of in situ studies of the surface V/III balance using the reflectance‐difference (RD) method during vacuum chemical epitaxy of (001) GaAs from arsine and triethylgallium. We have found a relationship between the RD signal and the V/III ratio, and we demonstrate the possibility for the use of this relationship for the optimization of growth. We have, by RD, detected a sharply defined, critical V/III ratio, below which the morphology and the photoluminescence intensity deteriorate dramatically, and which can be used to control the conversion from n‐type to p‐type conductivity. We believe that these observations will be of great importance for the in situ optimization of epitaxial growth, and in eliminating much of the uncertainties involved in reproducing surface V/III ratios.

Effects of pressure and temperature on RD detected growth oscillations

Abstract We report on the vacuum chemical epitaxy (VCE) growth of GaAs from triethylgallium and arsine at varying partial pressures of arsine and hydrogen. In situ, monolayer growth oscillations were, for the first time, detected in a hydrogen environment using reflectance difference (RD). These results offer the possibility to link surface mechanisms occuring during chemical beam epitaxy (CBE) with those taking place in metalorganic vapour phase epitaxy (MOVPE) and may lead to the observation of growth oscillations also during MOVPE. Finally, the behaviour of the RD signal as a function of substrate temperature is studied over a wider temperature interval than has previously been reported, giving further information about surface processes.

A compact vce growth system for in situ studies of epitaxy

Abstract A vacuum chemical epitaxy (VCE) equipment for growing epitaxial layers of GaAs from triethylgallium (TEG) and arsine (AsH3) as precursors has been developed. A novel inlet system consisting of two separate concentric nozzle rings with sixfold symmetry has been designed. The directed molecular beams from the nozzles are redistributed by the wall of the growth chamber which is at a temperature of about 250°C, thus avoiding pre-reactions of metalorganic (MO) gases and the condensation of As-related species. In this manner a uniform molecule density, growth rate and a multiple impinging of volatile group-V species, typical for VCE, is realized. The changeable wall geometry also allows work under chemical beam epitaxy (CBE) like conditions. Grown layers of GaAs have been characterized using photoluminescence (PL), deep level transient spectroscopy (DLTS), carrier concentration profile measurements and morphology studies. In situ measurements were conducted with the aid of line-of-sight quadrupole mass spectrometry (QMS) and reflectance difference (RD) measurements. RD made it possible to characterize the growth process, and to optimize growth parameters such as the V/III ratio, also the pressure is too high for reflection high-energy electron diffraction (RHEED). We have specifically studied AsH3 and TEG stabilized surfaces, and the transitions between these two types of surfaces, in the temperature range between 400 and 550°C.

Reflectance difference for in-situ characterization of surfaces and epitaxial growth of GaAs on (001) GaAs

Recent applications of spectroscopic phase modulated ellipsometry, from UV to IR, to the study of the growth of plasma deposited thin film semiconductors like amorphous (a-Si:H) and microcrystalline ((mu) c-Si) silicon are reviewed. The high sensitivity of this technique is emphasized. In the UV range, the ability of kinetic ellipsometry, with fast time resolution, to study the complex growth mechanism of (mu) c-Si is illustrated. In particular, the importance of hydrogen etching during (mu) c-Si growth is evidenced. In the IR, the hydrogen incorporation during a-Si:H growth can be precisely investigated. Photoelectronic quality a- Si:H films grow beneath a hydrogen rich overlayer (1-3 monolayers thick) containing SiH2, the hydrogen being bonded as SiH in the bulk material. 2.2 +/- 0.5 X 105 V/cm, which agrees very well with theory. thick. We show that this heterojunction is barely distinguishable in a PR measurement. Nevertheless, at room temperatutric field on the photoreflectance lineshape is discussed. The observed effect may be applied as an optical measurement of the electric field and the carrier concentration within a depth of about 17 nm from the surface/interface. phonon modes; InAs-like TO (226 cm-1), InAs-like LO (233 cm-1), GaAs-like TO (255 cm-1), and GaAs-like LO (270 cm-1), and one alloy disorder mode R* (244 cm-1) for InGaAs on InP. For all five Raman features stoichiometry, in terms of the RD response and the materials properties, which was recently demonstrated for VCE growth. Finally, we compare the quality and the character of real-time RD-detected growth oscillations as obtained for CBE, VCE, and MOVPE growth.

Reflection high energy electron diffraction and reflectance difference studies of surface anisotropy in InGaAs chemical beam epitaxy on flat and vicinal (001)GaAs

Abstract InGaAs quantum wells (QWs) were grown in a chemical beam epitaxy (CBE) machine with trimethylindium (TMI), triethylgallium (TEG) and tertiarybutylarsine (TBA) as precursors. Growth was monitored in-situ by reflectance difference (RD) and reflection high energy electron diffraction (RHEED), on both flat and vicinal (2° off in the 〈111〉 A direction) (001)GaAs substrates. The RD was monitored at 632.8 nm. At this wavelength the RD signal from a GaAs surface is primarily related to the absorption by Ga dimers. When InGaAs had been grown, both the average RD signal and the amplitude of the RD oscillations for the subsequent growth of GaAs increased significantly, compared to GaAs growth on GaAs. This In influence was found to persist even after the growth of 20–30 ML of pure GaAs. As a result we were able to monitor growth oscillations with RD and RHEED simultaneously during growth of quantum wells of InGaAs in GaAs. As a conclusion to these observations we suggest that the group III dimer bond concentration, detected in the RD signal, increases.