Low temperature PL

A strong argument in favor of the QC model is the observation of step-like features in the low-temperature PL spectrum of PS, as shown in Fig. 7.12, which correspond well with the energies of momentum-conserving phonons in crystal-... 

Fig. 4 Low temperature PL spectra (5.5 K) of (a) a GaN thin film with a thickness of 450 nm deposited at a substrate temperatme of 900 °C and a reactor pressure of 5 bar at a 345-fold excess of NH3 using N2 as carrier gas (100 seem) and (b) a commercial GaN thin film with a thickness of about 2 xm deposited in a standard process using TMG and NH3...

Fig. 3.25. (a) F-point band-to-band transition energies Eo (squares), Eo (triangles), and Eq (circles) of a PLD-grown ZnO thin film as a function of temperature obtained by SE. (b) Data for Eo from SE (solid symbols) and low-temperature PL (open symbols), and model calculations according to (3.29) (solid line). The inset enlarges the temperature range T < 120 K. 

A (002) XRC width of 9 arcmin in 0-20 scan has been achieved for MBE grown epilayers [36], Sharp and flat interface structures have been reported using the HRTEM technique [21], For the optical properties, low temperature PL excitonic emission widths around 18 meV [4,34] and a photoreflectance (PR) spin-orbit splitting structure [36] have been reported. Concerning the electrical quality, there have been almost no reliable data, because 3C-SiC layers used as substrates are usually conductive. 

The inverted Vj A), TeCil), Vj C) ordering of the valence subbands in bulk ZnO was confirmed by the detailed analysis of the Zeeman splitting of the free and bound excitons. The polarization properties and the angular dependence of the transition energies from excitons bound to ionized and neutral impurity centers indicated the T7 character of the upper A valence band. The obtained Tv effective g values are in good with theoretical calculations. We observed no low temperature PL transitions involving the Tg hole states from the B valence subband. 

The low temperature PL spectra of GaN layers grown on T63, T68 and the reference GaN layer are shown in Figure 6.25. For all three samples, the dominant emission peaks are related to donor-bound exciton recombination (D°X). The FWHMs of D°X for sample T63, T68 and reference GaN are 2.4, 3.8, and 3.0 meV, respectively, again consistent... 

Figure 6.25 Low temperature PL spectra of T63, T68 and reference sample. Reproduced from Y. Fu et at, J. Appl. Pbys., 99(3), Art. no. 033518. Copyright (2006), with permission from the American Institute of Physics...

We have studied the synthesis of InAs nano-sized crystalline precipitates in crystalline silicon by means of the co-implantation of As+ (245 keV, 5xl016 cm2) and In+ (350 keV, 4.5xl016 cm 2) at 500 °C and annealing at 900 °C for 45 min. RBS, TEM/TED and PL techniques were used to characterize the implanted layers. The density of the precipitates equals to 1.2xlOn cm 2. The most of the crystallites are from 2 nm to 8 nm in size. The precipitates are located within at the depths of 100 to 350 nm. A broad line at 1.3 pm is found in low-temperature PL spectra of co-implanted and annealed silicon crystals This line can be attributed to donor-acceptor pair recombination between In and As atoms which occupy the substitutional sites in the silicon lattice. 

Fig. 3 depicts low-temperature PL spectra of the implanted samples. A broad band at 0.92 eV with small intensity is observed in the as-implanted sample. It can be attributed to radiative recombination at defects induced by ion implantation. 

It should be underlined that the luminescence spectra of low-defect density nonpolar GaN material grown by optimized ELOG templates are dominated by the exciton-related emissions, and the defect-related recombinations have been significantly reduced [70]. Furthermore, for the bulk GaN material with nonpolar surfaces sliced from boules, which have been grown in the c direction, the low-defect density is reflected in a high optical quality [86, 100]. Namely, low temperature PL spectra in the NBE region show free-exciton emissions... 

In the low-temperature PL spectra of the nonpolar GaN-AlGaN MQWs, well-resolved exdtonic lines were visible (Figure 3.12a and b). 

Figure 8.1 Low-temperature PL spectrum of a 1-mm-thick c-plane GaN layer grown by HVPE.

Figure 8.2 Low-temperature PL spectrum of the same 1-mm-thickc-plane CaN layer obtained in different polarization geometries.

Figure 8.10 shows a low-temperature PL spectrum of a thick a-plane GaN layer grown by HVPE directly on r-plane sapphire [45]. like in the MOCVD layers, the spectrum is dominated by the D1 emission at 3.42 eV. The NBE emission is also resolved but now it is rather weak. The main difference, however, is the absence of D2 emission band at 3.29 eV. The emission at 3.35 eV (D3), if present, is very weak and presumably overlapped with the long low-energy tail of the D1 emission. As shown in the inset of Figure 8.10, both the D1 and NBE emissions exhibit a red shift with increasing layer thickness. 

As a result of the lower average density of the BSEs, the intensity of the 3.42- and 3.29-eV emissions is reduced and low-temperature PL spectra of ELO layers with [lT00]-oriented stripes are dominated by the NBE emission [67, 69]. 

Low-temperature PL spectra of (1122) layers grown by MOCVD are shown in Eigure 8.16 [66]. The spectrum of the planar layer is very similar to that of MOCVD-grown a-plane and m-plane layers, the D1 and D2 emissions dominate while the NBE emission is practically absent. The emission in the ELO layer with stripes perpendicular to the c-axis projection (ELO-90°) is clearly improved reflecting the improved structural quality of the material. Although the D1 emission is still present, the spectrum is now dominated by the NBE emission. In addition, the D2 emission is much weaker compared with the one in the planar layer. Also shown in Figure 8.16 is the PL spectrum of the ELO layer with stripes inclined at 45° to the c-axis projection (ELO-45°). Compared with the planar layer, the NBE emission in the ELO-45° layer is slightly enhanced and the D2 emission is reduced. The BSE-related emission... 

Optical properties of GaN plates with a semipolar (1122) surface sliced from thick HVPE layers as well as of homoepitaxial layers grown by MOCVD on such semipolar substrates have also been reported [106,107]. As in the case of the nonpolar bars, low-temperature PL spectra exhibit narrow DBE lines and well-resolved Xa and Xb EEs. However, the polarized PL spectra measured in backscattering geometry show some peculiarities, the most prominent of... 

Figure 3.13 Low-temperature PL spectra (raw and fitted data) of (a) nitrogen-doped and (b) undoped ZnO films. The inset shows the expanded spectral region of the near-band-edge PL response from the undoped sample. (After Ref [82].)...

To provide additional support for some of the peak assignments in the low-temperature PL spectrum of the high-quality ZnO substrate investigated, Teke et al. [50] studied the temperature evolution of these peaks. The temperature-dependent measurements were performed between 10 and 300 K. Figure 3.14 shows only the PL spectra for temperatures up to 160 K (at 10, 20, and up to 160 K with 20 K steps) because most of the important changes occur in this range. The spectrum for each temperature is displaced vertically for clarity. 

Figure4.4 (a) Low-temperature PL spectra of (1) ZnO reference layer and N-implanted samples with (2) 1 X 10 cm" and (3) 5 x 10 cm N concentrations after annealing at 800°C. DAP transition and its phonon replicas are visible for all samples. The emission at 3.286eV is the LO phonon replica of the donor-bound exciton.

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