Growth of GaN:Sb MBE-Layers
- PDF / 262,028 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 110 Downloads / 265 Views
Growth of GaN:Sb MBE-Layers P. Cristea, D.G. Ebling and K.W. Benz, Freiburg Materials Research Center, University of Freiburg, Stefan-Meier-Str. 21, 79104 Freiburg, Germany ABSTRACT The single crystalline growth of the GaNxSb1-x system is difficult due to the miscibility gap expected for nearly the whole composition range under thermodynamic equilibrium conditions. The gap is determined by the differences of the atomic radii and of the electro negativities for N and Sb. To overcome this problem crystal growth has to be performed under non-equilibrium conditions with kinetically controlled growth, as it is observed for molecular beam epitaxy (MBE) growth. A single crystalline MBE-growth within the miscibility gap has been demonstrated already in the GaAsxN1-x system exhibiting a similar large miscibility gap. GaN:Sblayers were grown on Si(111)-substrates by MBE using NH3 as a N-source and solid element sources for Ga and Sb. The parameter window for growth was limited due to side reactions like the decomposition of NH3, the desorption of (at high temperature volatile) compounds like Sb and GaSb or the reaction of Sb with NH3. The composition of the layers was analyzed by XRD and RBS. Antimony bulk concentrations of up to 1.6 % could be obtained in GaN. Optical characterization of the samples was performed by CL-measurements and indicate Sb-induced transitions in the 2.2 eV and 1.42 eV range. INTRODUCTION Currently, there is a high level of interest in group III-nitride semiconductors as well as in alloys with mixed group V-elements such as GaNxAs1-x [1] and GaNxP1-x [2]. The system GaNxSb1-x has been examined very rarely so far. Potential applications of such alloys are optical and opto-electronical devices in the whole visible- and IR-range. 7 6
direct semiconductor indirect semiconductor [4]
AlN
band-gap Eg [eV]
5 4 3
UV
GaN SiC InN
2
AlP GaP
AlAs
Si 1 IR
?
GaAs InP GaSb
0 -1 0,16
0,18
0,20
0,22
0,24
0,26
bonding length [nm]
Figure 1. Bonding length versus band gap energy of selected semiconductors. The dotted line indicate an assumed bowing of the band gap energy for GaNxSb1-x. The dashed line describes a calculated bowing for GaNxAs1-x [4]. I3.28.1
N As Sb
atom radius r [Å] 0.71 1.25 1.82
EN
∆r (N)
∆EN (N)
3.04 2.18 2.05
0.54 1.11
0.86 0.99
Table I. Comparison of atomic radii r and electro negativities EN of the group V elements N, As and Sb The large difference in lattice constants of GaN and GaAs of 20% (figure 1) leads to a nonlinear dependence of the band gap versus composition with a larger bowing parameter than for other III-V semiconductor alloys [3], which was also predicted by theoretical calculations [4]. Due to the higher difference in lattice constant between GaN and GaSb of 26% a stronger effect with a larger bowing parameter is expected for GaNxSb1-x indicated by the dotted line in figure 1. The large differences of atomic radii and electro negativities of group -V elements (Table I) lead to a miscibility gap under thermodynamic equilibrium conditions. The calculated mi
Data Loading...
