Thermal characterization of gallium arsenic nitride epilayer on gallium arsenide substrate using pulsed photothermal reflectance technique

Thermal conductivity of gallium arsenic nitride (GaAsN) epilayer on gallium arsenide (GaAs) substrate prepared by molecular beam epitaxy technique was measured using pulsed photothermal reflectance technique. Three-layer model incorporated thermal boundary resistance was applied to extract the thermal properties from the sample's photothermal response. Within the thickness ranging from 20 to 80 nm, no thickness dependent relationship with thermal conductivity of GaAsN epilayer was found, and the average thermal conductivity is approximately 27 W/mK at room temperature. The thermal boundary resistance at the Au/GaAsN interface is in the order of 10⁻⁸ m²K/W.     

Composition and temperature dependence of the direct band gap of GaAs1−xNx (0≤x≤0.0232) using contactless electroreflectance

The composition and temperature dependence (20K<T<380K) of the direct gap, E₀, of a series of GaAs_1−xN_x/GaAs (0≤x≤0.0232) samples has been measured using contactless electroreflectance. Our results for the composition dependence of E₀ are different in relation to a recent experiment [W.G. Bi and C.W Tu, Appl. Phys. Lett. 70, 1608 (1997)]. In contrast to previously reported results, we find that the temperature dependence of the direct gap is in fact dependent on N composition and that the parameters which describe the temperature dependence of the band gap lie between those of GaAs and GaN.     

MOVPE growth of GaAsN: surface study by AFM and optical properties

We report on the growth of GaAs_1−xN_x thin films on GaAs substrates (2° off) by metalorganic vapor-phase epitaxy, in the temperature range 500–600°C. A mixture of N₂ and H₂ was used as the carrier gas. Using dimethylhydrazine as nitrogen source, we incorporated up to 3.5% of nitrogen, at 530°C. The growth condition dependence of nitrogen content was studied, and it reveals a distribution coefficient 350 times lower for nitrogen than for arsine at 530°C. Nitrogen incorporation is controlled by surface kinetics. The evolution of surface morphology has been investigated by atomic force microscopy as a function of the nitrogen composition and of growth temperature. For nitrogen content up to 2%, the GaAsN vicinal surface is characterized by a step–terrace structure with bunched steps, and the step edges straighten when increasing the growth temperature. For higher nitrogen content terraces are no longer observed and, above 3%, widely-spaced cross-hatch lines, characteristic of a partial relaxation of strain in the epilayers, appear. Optical properties were studied by low (7 K) and room-temperature photoluminescence and photoreflectance. As usual for this material, a degradation of optical characteristics is observed with increasing N content along with the evolution of surface morphology.     

The growth and properties of mixed group V nitrides

Bearing in mind the problems of finding a lattice-matched substrate for the growth of binary group III nitride films and the detrimental effect of the large activation energy associated with acceptors in GaN, we propose the study of the alloy system AlGaAsN. We predict that it may be possible to obtain a direct gap alloy, with a band gap as wide as 2.8eV, which is lattice-matched to silicon substrates. The paper reports our attempts to grow GaAsN alloy films by molecular beam epitaxy on either GaAs or GaP substrates, using a radio frequency plasma source to supply active nitrogen. Auger electron spectra demonstrate that it is possible to incorporate several tens of percent of nitrogen into GaAs films, though x-ray diffraction measurements show that such films contain mixed binary phases rather than true alloys. An interesting observation concerns the fact that it is possible to control the crystal structure of GaN films by the application of an As flux during growth. In films grown at 620°C a high As flux tends to increase the proportion of cubic GaN while also resulting in the incorporation of GaAs. Films grown at 700°C show no evidence for GaAs incorporation; at this temperature, it is possible to grow either purely cubic or purely hexagonal GaN depending on the presence or absence of the As beam.     

Raman scattering study of a GaAsN epitaxial layer

Raman scattering study of a dilute GaAsN epitaxy layer was carried out at variable temperature and pressure. The localization due to the presence of the N atoms is responsible for the small correlation length in the GaAsN alloy, which is also evident from the broadening and asymmetry of the LO mode of the GaAs-like Raman band. The temperature dependence of the correlation length was analyzed. Nitrogen-induced localization also has a strong influence on the pressure dependence of the Born's effective dynamic charge e*.     

Resonant Raman Scattering and Photoluminescence Emissions from Above Bandgap Levels in Dilute GaAsN Alloys

利用显微光致发光技术,观测到了N含量为0.1%,0.22%,0.36%和0.62%的GaAsN合金的E0,E0 △0和E 能级的光致发光峰.共振喇曼散射谱进一步证实了这些发光峰来源于所研究材料的本征能级,而不是来源于GaAsN合金中的一些局域激子发射.随着N组分的增加,E0 △0和E 能级分别向低能和高能方向移动并在N组分为0.16%时发生交错.文中提出了一种少量等电子掺杂和显微光致发光谱相结合的方法来直接观测半导体材料带边以上的跃迁能级,尽管光致发光谱通常没有用来观测这些能级位置.     

A recombination center in p-type GaAsN grown by chemical beam epitaxy

The double carrier pulse deep level transient spectroscopy (DLTS) technique is used to characterize recombination centers in p-type GaAsN grown by chemical beam epitaxy. The DLTS peak height of a shallow hole trap H1, at 0.052 eV from the valence band edge of GaAsN, decreases by the injection of both majority and minority carriers for various values of voltage and duration of the second pulse. Although the trap is shallow, its capture cross section is relatively large to capture electrons and holes. The decrease in the number of traps is explained by the electron-hole recombination process. This confirms, for the first time, that H1 is a recombination center in p-type GaAsN.     

Nanometer-scale studies of nitride/arsenide heterostructures produced by nitrogen plasma exposure of GaAs

We have investigated the nanometer-scale structure and electronic properties of nitride/arsenide superlattices produced by nitridation of a molecular beam epitaxially grown GaAs surface. Using cross-sectional scanning tunneling microscopy and spectroscopy, we find that the nitrided layers are not continuous films, but consist of groups of atomic-scale defects and larger clusters. We identify the defects and clusters as N_As and GaN with dilute As concentration, respectively. Thus, the nitrided regions consist of alloys from both sides of the miscibility gap predicted for the GaAsN system. In addition, spectroscopy on the clusters reveals an upward shift of the band edges and band gap narrowing, with significant change in the conduction band structure. We estimate the contribution of strain to band gap narrowing in terms of an elasticity calculation for a coherently strained spherical GaN cluster embedded in GaAs.     

低N含量GaAsN材料的共振喇曼散射及其带边以上的光致发光光谱

利用显微光致发光技术,观测到了N含量为0.1%,0.22%,0.36%和0.62%的GaAsN合金的E0,E0+△0和E+能级的光致发光峰.共振喇曼散射谱进一步证实了这些发光峰来源于所研究材料的本征能级,而不是来源于GaAsN合金中的一些局域激子发射.随着N组分的增加,E0+△0和E+能级分别向低能和高能方向移动并在N组分为0.16%时发生交错.文中提出了一种少量等电子掺杂和显微光致发光谱相结合的方法来直接观测半导体材料带边以上的跃迁能级,尽管光致发光谱通常没有用来观测这些能级位置.     

Structural properties of GaAsN grown on (001) GaAs by metalorganic molecular beam epitaxy

Detailed transmission electron microscopy (TEM) and transmission electron diffraction (TED) examination has been made of metalorganic molecular beam epitaxial GaAsN layers grown on (001) GaAs substrates. TEM results show that lateral composition modulation occurs in the GaAs_1−xN_x layer (x 6.75%). It is shown that increasing N composition and Se (dopant) concentration leads to poor crystallinity. It is also shown that the addition of Se increases N composition. Atomic force microscopy (AFM) results show that the surfaces of the samples experience a morphological change from faceting to islanding, as the N composition and Se concentration increase. Based on the TEM and AFM results, a simple model is given to explain the formation of the lateral composition modulation.