n‐type silicon‐doped epitaxial layers of gallium arsenide grown by molecular‐beam epitaxy (MBE) or metal‐organo chemical vapor deposition (MOCVD) have been investigated by measurements of the Hall effect and the strengths of the localized vibrational modes (LVM) of silicon impurities using both Fourier transform absorption spectroscopy and Raman scattering at an excitation energy of 3 eV close to the E1 band gap. Lines from Si(Ga) donors, Si(As) acceptors, Si(Ga)‐Si(As) pairs, and Si‐X, a complex of silicon with a native defect, were detected and correlated for the two techniques. The maximum carrier concentration [n] found for samples grown under standard conditions was 5.5×1018 cm−3. At higher doping levels Si‐X becomes dominant and acts as an acceptor, so reducing [n]. An integrated absorption of 1 cm−2 in the Si(Ga) LVM line corresponds to 5.0±4×1016 atoms cm−3: a similar calibration applies to the Si(As) line, but for Si‐X, an absorption of 1 cm−2 corresponds to only 2.7±1.0×1016 defects cm−3. Possib...

The calibration of the strength of the localized vibrational modes of silicon impurities in epitaxial GaAs revealed by infrared absorption and Raman scattering

Secondary Ion Mass Spectrometry (SIMS) is a mature surface analysis technique with a vast range of applications in Materials Science. In this review article the SIMS process is described, the fundamental SIMS equations are derived and the main terminology is explained. The issue of quantification is addressed. The various modes of SIMS analysis including static SIMS, imaging SIMS, depth profiling SIMS and three-dimensional (3D) SIMS are discussed as are specialized analysis strategies such as the imaging of shallow bevels and cross-sections and reverse side analysis. SIMS is shown to be a useful sample preparation tool based on ion beam milling (with SIMS and Scanning Electron Microscopy (SEM) analysis providing end-point detection). The case studies shown illustrate the application of SIMS to several important materials including semiconductors, superconductors, glass, stainless steel, micrometeoroids, solid oxide fuel cell components, museum artifacts, aerospace alloys and biomaterials. Strategies for introducing SIMS into undergraduate education and thus increasing awareness are described. Finally some informed guesses are made as to the future directions of SIMS.

Applications of Secondary Ion Mass Spectrometry (SIMS) in Materials Science

Dopant segregation in the well region of a multiple quantum well intersubband photodetector can cause an asymmetry in the observed forward and reverse current‐voltage characteristics. We compensate for the segregation by shifting the position of the Si δ doping in the well and model the effect with good agreement for a range of shift values. For samples grown at a substrate temperature of 605 °C, we find that the observed behavior is best described by assuming that the Si δ‐doping profile smears in the growth direction resulting in an asymmetric broadening of about 27 A.

Segregation of Si δ doping in GaAs-AlGaAs quantum wells and the cause of the asymmetry in the current-voltage characteristics of intersubband infrared detectors

HgCdTe 2D arrays are needed in both medium (MW) and long (LW) wavebands for imaging, search, and track and guidance applications. Often the detector is the performance-limiting component in the system, and it is necessary to use detectors with very low excess noise and few defective pixels. Normally the detector is cooled sufficiently to freeze-out thermally generated leakage currents, so the main interest is to understand the mechanisms that determine the general detector performance and the cause of defective pixels. This paper describes the detector technology and the ion beam junction-forming process. The fundamental performance limits of homojunction HgCdTe technology and the doping levels needed to produce a detector with impact-ionization limited performance are discussed. Extensive studies have been made on defective pixels in long wavelength arrays and some technologies for reducing them are described here. Defective pixels have been found to be associated with material dislocations crossing the p-n junction and a model has been proposed for the noise-generating mechanism.

Summary of HgCdTe 2D array technology in the U.K.

High-quality GaMnAs films grown with arsenic dimers

Si atomic plane or delta ( delta )-doping of GaAs during MBE has been investigated using SIMS profiling optimised for high depth resolution. For layers in which almost all the Si atoms act as donors, post-growth diffusion occurs at the growth temperature with a diffusion coefficient estimated to be 9*10-17 cm2 s-1 at a substrate temperature of 550 degrees C. At temperatures greater than about 550 degrees C, a marked preferential migration towards the surface is observed, which may be due to surface segregation or possibly enhanced diffusion.

http://iopscience.iop.org/article/10.1088/0268-1242/3/6/019/pdf

Migration of Si in δ-doped GaAs

Delta-doping of GaAs and Al0.33Ga0.67As with Sn, Si and Be: a comparative study

A GaAs layer grown by MBE at a substrate temperature of 520 degrees C and containing three delta -doped planes with Si concentrations of 0.4, 1 and 4*1013 atoms/cm2 has been post-growth annealed in a furnace, up to temperatures of 648 degrees C. Secondary ion mass spectroscopy (SIMS) and capacitance voltage (cv) measurements have been carried out to measure profile-broadening. The most lightly doped plane gave a near-Gaussian diffusion profile with a diffusion coefficient comparable with literature values for simple diffusion of isolated SiGa atoms. The more heavily doped planes exhibit a complex profile shape with two components, a proportion of the atoms being confined to the original plane, together with an almost square-shaped profile of fast-diffusing atoms. Comparison of the CV and SIMS data suggests that formation of Si islands is taking place during deposition of the delta -doped plane, giving electrically inactive atoms which can subsequently diffuse into the surrounding GaAs during heat-treatment. This model is supported by preliminary local vibrational mode measurements which have been made on a set of multiplane samples.

https://iopscience.iop.org/article/10.1088/0268-1242/4/12/021/pdf

Post-growth diffusion of Si in delta -doped GaAs grown by MBE

In two recent review papers on metal organic vapour phase epitaxy (MOVPE) of cadmium mercury telluride (CMT) particular emphasis was placed on the crucial importance of doping studies to the realization of future device structures Irvine et al. (1991) and Tribowet (1991). If the full potential of MOVPE growth of CMT is to be realized then extrinsic doping of heterostructures is required. If the doping and composition junctions can be grown with the correct degree of grading then this will create the potential for the production of device structures leading to either improved performance and/or increased operating temperatures. This papers reviews published doping studies and also presents some recent results on both acceptor and donor doping studies carried out by the authors. In the latter studies, interdiffused multilayer process (IMP) growth of CMT has been performed at approximately=360 degrees C using dimethyl cadmium (DMC) and di-isopropyl tellurium (DIPT) as the MO precursors while the Hg overpressure was provided by a heated elemental source. Alternative acceptor doping sources to arsine have been investigated including phosphine, triphenyl arsenic, and phenyl arsenic of which the latter appears to be most suitable. Iodine has continued to show the donor dopant potential in CMT that it exhibited with higher-temperature ( approximately=400 degrees C) MOVPE growth using di-ethyl tellurium (DET). Characterization of fully doped structures is described.

J B Clegg

Papers

Migration of Si in δ-doped GaAs

Delta-doping of GaAs and Al0.33Ga0.67As with Sn, Si and Be: a comparative study

Post-growth diffusion of Si in delta -doped GaAs grown by MBE

Doping studies in MOVPE-grown CdxHg1-xTe

Si migration effects in GaAs/(Al,Ga)As heterojunction and δ-doped structures