Thumbnailed Figures of MIJ-NSR Volume 6, Article 2

Figures

Figure 1

Compositional dependence of the band gap energy of GaN_xAs_1-x. The points represent experimental data, corrected to room temperature. The lines show results of theoretical calculations. The legend indicates references and the measurements or theoretical approaches used. The bowing coefficient deduced by the dielectric model calculations (the blue dotted line) is 20 eV.

Figure 2

Electroreflectance spectra at RT for a 2 µm thick GaAsN film on a GaAs substrate. The band gap transition (E₀) at 1.19 eV as well as the transition from the spin-orbit split-off VB (E₀+

₀) at 1.52 eV are easily seen. An additional weak feature (E₊) at 1.83 eV is more clearly seen in the second spectrum at 10x and offset for clarity. The fitted line shape for the E₀+

₀ and E₊ transitions are shown with dashed lines and offset for clarity. (After Ref. [29])

Figure 3

Electroreflectance spectra at RT for thick GaAsN (a)-(h) and GaInNAs [(i) and (j)] films grown on a GaAs substrate. For GaNAs samples, the nitrogen composition ranges from x=0 (a) to x=2.8 % (h). For GaInAsN samples, the compositions are Ga_0.95In_0.05As_0.987N_0.013 (i) and Ga_0.92In_0.08As_0.978N_0.022(j). (After Ref. [29])

Figure 4

Compositional dependence of the E_- and E₊ transition energies. The points represent the experimental data. The lines are a guide to the eye. The legend indicates the references.

Figure 5a

Effects of hydrostatic pressure on the energies of the E_- and E₊ transitions in GaNAs. The blue triangles represent the RT photoreflectance (PR) data [31] for a GaNAs epitaxial layer with %N=1.5%. The blue lines are results from the BA calculations for the same structure [31]. The dashed and dashed-dotted lines represent the pressure dependencies of the

CB edge (E) of GaAs and N-related level (E_N), respectively. The red lines show results of the LDA calculations [42] for GaNAs with %N=0.8%.

Figure 5b

Effects of hydrostatic pressure on the energies of the E_- and E₊ transitions in GaInNAs. The blue triangles represent the RT photoreflectance data [30] obtained for a GaInNAs epitaxial layer with %In = 5% and %N=1.2%. The blue lines show results from the BA calculations for the same structure [30], assuming a linear pressure dependence of the

CB edge (~100 meV/GPa) and the N-related level (~15 meV/GPa), shown by dashed-dotted lines. The red dots show the PL data from Ref. 33 for a thick lattice-matched GaInNAs epilayer with %In = 7% and %N= 2%, for comparison. The red line represents the results of the LDA calculations [33] for the same structure, which are offset by 1.14 eV to achieve the agreement with the experiment at ambient pressure.

Figure 6

Schematic of dispersion relations for the E_- and E₊ subbands based on the band anticrossing model [32]. The unperturbed energies of the N-related level (E_N) and the GaAs conduction band (E) are also shown.

Figure 7

Temperature dependent shift of the band gap energy detected via (a) absorption in the GaNAs/GaAs epilayers, according to Ref. [45], and (b) via photoluminescence in GaInNAs/GaAs single QW structures, according to Ref. [46].

Figure 8

Change in the energy position of the E₁ transition as a function of N composition.

Figure 9

(a) The ODCR spectrum arising from the GaAs layers (x=0) in the GaAsN/GaAs QWs structures when the excitation energy was tuned above the GaAs bandgap. (b)-(c) The ODCR spectra of the GaAsN QWs, when the excitation photon energy was tuned at 1.475 eV, i.e. below the GaAs bandgap but above the bandgap of the GaAsN QWs. The dashed lines represent experimental data. The solid lines are the fit curves [49] [58] by using effective mass values specified in the Figure.

Figure 10

Compositional dependence of the electron effective mass in the GaNAs alloy. The red dots represent experimentally determined values in GaNAs/GaAs QWs via the ODCR measurements [49]. The open triangles represent the values indirectly deduced by analyzing the quantum confinement energies in the GaNAs/GaAs QWs, from Ref. [51]. The solid blue lines show predictions based on the BA model [53]. The dashed green lines represent the results of the k·p calculations [39].

Figure 11

Experimental reflectivity spectra (solid lines) for two InGaNAs:Se samples with distinctly different electron concentrations. The dashed lines show fit [50] with indicated effective mass values (Courtesy C. Skierbiszewski).

Figure 12

Dependence of the measured electron effective mass on the electron concentration. The dots are experimental data [50]. The lines are a guide for the eye.

Figure 13

Compositional dependence of the VB edge for strain-free GaNAs predicted by various theoretical calculations. The legend indicates the references.

Figure 14

Spectral dependence of the PL decay time (the dots) detected at 2K from the single GaN_0.012As_0.988epilayer (a) and the GaN_0.011As_0.989/GaAs MQW structure (b). The PL spectra from the same structures are also shown by solid lines, for easy reference.

Figure 15

Schematic band diagrams of the quantum structures with the type I and type II band alignment and their expected properties [58]. The arrows show the dominant PL recombination transitions for each structure, i.e. direct in space for the type I transitions (the solid arrow) and indirect in space for the type II transitions (the dashed arrow).

Figure 16

Schematic diagram of band lineup for GaInAs and GaNAs. The use of strain for the horizontal axis allows to demonstrate the effect of nitrogen on the band gap edges [12] (increasing the In content leads to a compressive strain, whereas increasing the N content causes a tensile strain). The arrows show the effect of nitrogen on the CB and VB edges of GaInAs. Dotted line and arrow are related to the theoretical predictions based on the dielectric model. Solid green arrow assumes the N-induced increase in the VB edge of GaInNAs, as predicted by the LDA [10] or tight-binding [39] calculations for the GaNAs alloy (shown by solid red line).

Figure 17

PL (solid lines) and PLE (dotted lines) spectra of the GaNAs/GaAs MQWs with x=1.2% (red lines) and x=2% (blue lines), respectively.

Figure 18

(a) Temperature-dependent PL and PLE spectra of a GaN_xAs_1-x/GaAs MQW structure with x=1.2%. The PLE spectra are normalized to demonstrate the minor shift of the GaNAs bandgap between 20K and 80 K. (b) Temperature dependence of the PL maximum position measured from the same structure.

Figure 19

Typical spectral dependence of the PL decay time (the dots) detected at 2K from GaNAs, demonstrated with the example of a GaN_0.028As_0.972/GaAs MQW sample. The insert shows the representative PL decay curves measured at two specified PL energies.

Figure 20

Typical PL spectrum detected at 2K from a GaInNAs/GaAs QW.

Figure 21

Dark field image of the as-grown GaInNAs/GaAs SQW that reveals non-uniform strain distribution in the structure (Courtesy L. Grenouillet).

Figure 22

Bright field XTEM micrographs of a RTA-annealed sample consisting of two-period Ga_0.7In_0.3N_0.02As_0.98/GaAs QWs (the bottom two layers) and two period Ga_0.7In_0.3As/GaAs QWs (the upper two layers). Note the higher lateral undulation for the N-containing QWs in spite of the lower average strain (Courtesy H. P. Xin).

Figure 23

The PL spectra of three GaNAs/GaAs QW structures with different nitrogen composition, to demonstrate the drastic decrease of the PL intensity with increasing N composition in the alloy.

Figure 24

RTA-induced improvement of the optical quality of the GaN_0.011As_0.989/GaAs MQW structure grown at 580 ^°C. The blue and red lines are related to the as-grown and RTA-treated samples, respectively. The solid lines represent PL spectra, the dotted lines represent PLE spectra. The minor change in the spectral position of the PLE spectra demonstrates a high thermal stability of the structure.

Figure 25

(a) GaNAs ODMR spectrum taken at 5K and 9.218 GHz. (b) The simulated ODMR curve for the single line of g=2.03. (c) The quadruplet ODMR spectrum after subtracting the curve b from curve a. The simulated ODMR spectrum for the As_Ga antisite (d) and for the Ga_i interstitial (e). The ODMR signals are negative, but are shown here positive for easy viewing.

Figure 26

ODMR spectra detected from the LT-grown GaN_0.028As_0.972/GaAs MQW structure before (the red line) and after (the blue line) RTA, respectively. Two negative ODMR signals as given in Figure 25 are clearly detected in the as-grown structure, but almost disappear after RTA.

last updated Thursday, January 25, 2001 4:55:49 PM.