The dependence of the In-incorporation efficiency and the optical properties of MOVPE-grown GaInN/GaN-heterostructures on various growth parameters has been investigated. A significant improvement of the In-incorporation rate could be obtained by increasing the growth rate and reducing the H2-partial pressure in the MOVPE reactor. However, GaInN layers with a high In-content typically show an additional low energy photoluminescence peak, whose distance to the band-edge increases with increasing In-content. For GaInN/GaN quantum wells with an In-content of approximately 12%, an increase of the well thickness is accompanied by a significant line broadening and a large increase of the Stokes shift between the emission peak and the band edge determined by photothermal deflection spectroscopy. With a further increase of the thickness of the GaInN layer, a second GaInN-correlated emission peak emerges. To elucidate the nature of these optical transitions, power-dependent as well as time-resolved photoluminescence measurements have been performed and compared to the results of scanning transmission electron microscopy.

We studied by deep level transient spectroscopy (DLTS) and capacitance-voltage (CV) measurements the effects of doping (Zn, S), nitrogen implantation and annealing of n-type GaN grown on sapphire by MOVPE. The DLTS spectra of the as grown samples show two defect levels which are assumed to be identical with recently reported levels [10, 11]. In N-implanted GaN a third level is introduced which is not detectable in our as grown samples. This levels concentration follows the increasing N-implantation density. The depth profiles of its concentration correlate with the distribution of implantation defects expected from Monte-Carlo simulation. After annealing at 900°C for 60s the additional defect level vanishes. The DLTS spectrum then resembles those of annealed as grown samples. The n-type carrier concentration (CV measurements) increases in samples with low N-implantation dose. This implantation effect can be removed also with the RTA step. The increasing carrier concentration provides evidence that the N vacancy is a donor in GaN. For Zn and S doped GaN deep defect levels has been found, which are reported here.

Two positive ODMR resonances are commonly observed on a luminescence band in GaN at 2.2 eV, one identified as a shallow donor, the other currently unidentified. We here report a study of their dependencies on a variety of experimental parameters, including microwave modulation frequency, microwave power, photoexcitation power and photoexcitation energy. ODMR simulations using two theoretical models are compared to experimental results which are consistent with spin-dependent recombination between the two defects, assuming the donor has a spin-lattice relaxation time shorter than the spin-dependent recombination lifetime. The photoexcitation energy dependence suggests that the spin-dependent recombination associated with the 2.2 eV band is not the same recombination that is responsible for the luminescence. This supports the two stage model put forth by Glaser et al. for the luminescence process.

GaInN/GaN heterostructures and quantum wells have been grown by low pressure metalorganic vapor phase epitaxy on sapphire using an AIN nucleation layer. We found a significant In incorporation only for growth temperatures of 700°C, although still very high In/Ga ratios in the gas phase had to be adjusted. The In content could be increased by reducing the H2/N2 flow ratio in the main carrier gas. GaInN layers typically show two lines in low temperature photoluminescence which are identified as excitonic-like (high energy peak) and impurity-related-like (low energy) by time-resolved spectroscopy. Quantum wells with a thickness between 8 and 0.5 nm showed only one emission line. The peak of the thinnest wells shows excitonic-like behaviour, whereas we found a smooth transition to an impurity-related-like type with increasing thickness. By scanning transmission electron microscopy studies we found indications for composition fluctuations in these thicker quantum wells which may cause localization effects for the excitons and thus be responsible for the observed optical spectra.

We analyze the Zeeman effect of the 4/13/2 → 4/15/2 transition of Er3+ in GaAs:Er,O grown by metal-organic vapor-phase epitaxy. The photoluminescence spectrum has been assigned previously to one specific Er-O complex. The dominant optical transition at 1538 nm (6499.5 cm−1), which shows a full width at half maximum of only 0.05 cm−1, has been investigated by high-resolution Zeeman spectroscopy. A highly anisotropic Zeeman pattern is found which indicates the low symmetry of the underlying complex. A detailed analysis shows that the defect has a predominant rhombic symmetry C 2v ,. Additionally, smaller contributions of a crystal field with a monoclinic symmetry C lh are found. The results provide further arguments that an ErO2 complex is the responsible center observed.

We performed low temperature photocurrent and photoluminescence excitation spectroscopy on tensile and compressively strained GaxIn1-xAs/GaInAsP quantum well layers to determine the band offset of the heterojunction (0.3 <XGa < 0.7). The ratio of the conduction band discontinuity to the heavy hole discontinuity has been obtained from well to barrier transitions and is found to be about 35/65 for gallium contents between 0.4 and 0.6. We obtained the effective heavy hole mass by comparison of PLE transition energies with calculations of the subband levels. We observe that the effective heavy hole mass increases with the gallium content from 0.3 m0 for XGa = 0.31 to about 0.45m0 for XGa = 0.55.

Different III-V compound semiconductors have been doped with the rare earth (RE) elements Yb, Er, and Tm using atmospheric pressure metalorganic vapor phase epitaxy. Best results have been obtained using the novel metalorganic compounds tris-isopropyl-cyclopentadienyl-RE as precursors which have an acceptable vapor pressure and can be used as liquids at bubbler temperatures of 60°-90°C. Only Yb has been found to occupy a regular lattice site in InP, whereas the other RE show complex optical spectra because of their incorporation in form of different centers and clusters.

We investigate the excitation mechanism of the characteristic 4f luminescence 3 H5 →3H6 of Tm3+ in GaAs by photoluminescence excitation spectroscopy. This luminescence transition is also used to study the incorporation of thulium into the GaAs lattice by angular dependent Zeeman spectroscopy.

The growth of GaAs epilayers on Si should combine the advantages of both materials. The lattice mismatch and the difference in thermal expansion coefficients, however, result in the yet unsolved problems of high dislocation density and thermal stress in the GaAs layer. Recently, considerable improvements have been achieved by a ‘thermal cyclic growth’ (TCG) process. In this study we focus on the reduction of high defect concentration and dislocation density. The improvement of the epilayer quality is verified by DLTS, PL and DCXD. Results of TEM and DLTS measurements lead to the identification of a dislocation related defect.

We present highly resolved photoluminescence studies on heat-treated nominally undoped InP, which was either unprotected or protected by SiO2 or Si3N4 caps during the annealing procedures. Annealing of InP above 350°C leads to six different sharp emissions in the wavelength range between 8790 and 8900 Å, which are not observed at 4 K in Zn-doped or Fe-doped samples. Based on temperature-dependent photoluminescence studies, time-resolved measurements and preliminary magnetic field studies we ascribe these emissions to isoelectronic bound exciton transitions. It is also shown that the two emissions at 8883 Å (11254 cm-1) (E) and 8889 Å (11246 cm-1) (F) belong to one center. We observe that the lines not only depend on the heat treatment but also on some unintentionally incorporated or residual impurities of a low concentration level. Possible candidates are discussed.

The 0.5 eV (2.5 μm 4000 cm1) emission band in InP has been studied by optical spectroscopy. By the use of Fourier-transform-infrared photoluminescence we have been able to observe at least a three-fold fine structure in the zero-phonon transitions at ∼ 4300 cm−1 which are studied at different temperatures. Based on the fine structure and the long decay time of 1.1 ms we ascribe the 0.5 eV emission to the 4T1 → 6A1 spin-flip transition of Fe3+. The excitation spectrum of this Fe3+-related emission shows a characteristic fine structure at ∼ 1.13 eV which belongs to a charge-transfer process of the type: Fe3+ + hv (1.13 eV) → [Fe2+, bound hole]. We discuss the excitation mechanism of the 0.5 eV emission by charge-transfer states and compare the results with an emission at 3057 cm1 in GaAs, which we attribute to the same Fe3+ transition (decay time: 1.9 ms).

In the present paper, optical absorption studies on the neutral charge state of the double acceptor zinc in silicon are presented. Measurements were carried out in the mid infrared (MIR) and in the near infrared (NIR) region. The MIR absorption spectra show the excitation series of an effective-masslike hole, from which the Zn° level position is calculated to be at Ev + 319. 1 meV. A splitting of the ground state into 3 sublevels is assigned to hole-hole coupling and crystal-field splitting. Absorption spectra obtained in the NIR are interpreted in terms of an A° X-type bound exciton.

We observe in photoconductivity (PC) measurements EMT-like excited states of the pseudodonor CrB, which are responsible for the capture of free electrons due to their short lifetime. The energetic position of the ground state can be located at Ev + (292 ± 5) meV. A finestructure of the (CrB)° transition consisting of at least 15 components is observed in PC and high-resolution Fourier transform photoluminescence. In acceptor-free silicon a step in photoconductivity at 205 ± 10 meV is ascribed to interstitial Cr, whereas a second step at ~ 425 meV could be due to substitutional Cr.

Recently developed tunable color center lasers allow to extend the experimental technique of excitation spectroscopy to the 1–2 μm region. This spectral range is of special interest for the study of luminescent defects in silicon. We discuss the color center laser systems available at present and their application to defect spectroscopy. As an example, results on the 0.767 eV (P line) defect in silicon are presented. Excitation spectroscopy reveals several high lying excited electronic states. They are interpreted as effective—mass—like states of a pseudo-donor with an ionization energy of 34.3 meV.

We report five photoluminescence lines N1 through N5 in silicon which emerge after sequential nitrogen and carbon implantation. Studied is in particular the 0.7456 eV (N1) electronic-vibronic spectrum. Single nitrogen and carbon atoms in the defect are identified by isotope shifts of the no-phonon transition and of a local mode satellite with vibration quantum energy ħω= 122.9 meV. Uniaxial stress or Zeeman measurements yield monoclinic I (C1h) or trigonal (C3v) symmetry, respectively, of the optical defect. Comparing the energy of the local mode and its isotope effects with recent literature data on the nitrogen 963 cm−1 IR vibrational absorption line we discuss a defect model involving a substitutional nitrogen atom modified by an interstitial carbon atom.