Band Gap of Hexagonal InN and InGaN Alloys (original) (raw)
Related papers
2009
InGaN based, blue and green light emitting diodes (LEDs) have been successfully produced over the past decade. But the progress of these LEDs is often limited by the fundamental problems of InGaN such as differences in lattice constants, thermal expansion coefficients and physical properties between InN and GaN. This difficulty could be addressed by studying pure InN and In x Ga 1-x N alloys. In this context Ga-rich In x Ga 1-x N (x≤ 0.4) epilayers were grown by metal organic chemical vapor deposition (MOCVD). X-ray diffraction (XRD) measurements showed In x Ga 1-x N films with x= 0.37 had single phase. Phase separation occurred for x ~ 0.4. To understand the issue of phase separation in Ga-rich In x Ga 1-x N, studies on growth of pure InN and In-rich In x Ga 1-x N alloys were carried out. InN and In-rich In x Ga 1-x N (x~0.97-0.40) epilayers were grown on AlN/Al 2 O 3 templates. A Hall mobility of 1400 cm 2 /Vs with a carrier concentration of 7x10 18 cm-3 was observed for InN epilayers grown on AlN templates. Photoluminescence (PL) emission spectra revealed a band to band emission peak at ~0.75 eV for InN. This peak shifted to 1.15 eV when In content was varied from 1.0 to 0.63 in In-rich In x Ga 1-x N epilayers. After growth parameter optimization of In-rich In x Ga 1-x N alloys with (x= 0.97-0.40) were successfully grown without phase separation. Effects of Mg doping on the PL properties of InN epilayers grown on GaN/Al 2 O 3 templates were investigated. An emission line at ~ 0.76 eV, which was absent in undoped InN epilayers and was about 60 meV below the band edge emission peak at ~ 0.82 eV, was observed to be the dominant emission in Mg-doped InN epilayers. PL peak position and the temperature dependent emission intensity corroborated each other and suggested that Mg acceptor level in InN is about 60 meV above the valance band maximum. Strain effects on the emission properties of InGaN/GaN multiple quantum wells (MQWs) were studied using a single blue LED wafer possessing a continuous variation in compressive strain. EL emission peak position of LEDs varies linearly with the biaxial strain; a coefficient of 19 meV/GPa, characterizes the relationship between the band gap energy and biaxial stress of In 0.2 Ga 0.8 N/GaN MQWs.
Small band gap bowing in In1−xGaxN alloys
Applied Physics Letters, 2002
High-quality wurtzite-structured In-rich In 1-x Ga x N films (0 ≤ x ≤ 0.5) have been grown on sapphire substrates by molecular-beam epitaxy. Their optical properties were characterized by optical absorption and photoluminescence spectroscopy. The investigation reveals that the narrow fundamental bandgap for InN is near 0.8eV and that the bandgap increases with increasing Ga content. Combined with previously reported results on the Ga-rich side, the bandgap versus composition plot for In 1-x Ga x N alloys is well fit with a bowing parameter of ~ 1.4 eV. The direct bandgap of the In 1-x Ga x N system covers a very broad spectral region ranging from near-infrared to near-ultraviolet.
Structure and electronic properties of InN and In-rich group III-nitride alloys
Journal of Physics D: Applied Physics, 2006
The experimental study of InN and In-rich InGaN by a number of structural, optical and electrical methods is reviewed. Recent advances in thin film growth have produced single crystal epitaxial layers of InN which are similar in structural quality to GaN films made under similar conditions and which can have electron concentrations below 1 × 10 18 cm −3 and mobilities exceeding 2000 cm 2 (Vs) −1 . Optical absorption, photoluminescence, photo-modulated reflectance and soft x-ray spectroscopy measurements were used to establish that the room temperature band gap of InN is 0.67 ± 0.05 eV. Experimental measurements of the electron effective mass in InN are presented and interpreted in terms of a non-parabolic conduction band caused by the k · p interaction across the narrow gap. Energetic particle irradiation is shown to be an effective method to control the electron concentration, n, in undoped InN. Optical studies of irradiated InN reveal a large Burstein-Moss shift of the absorption edge with increasing n. Fundamental studies of the energy levels of defects in InN and of electron transport are also reviewed. Finally, the current experimental evidence for p-type activity in Mg-doped InN is evaluated.
Phys Rev B, 2002
The electronic structure of In x Ga 1Ϫx N alloys with (0рxр0.3) has been studied using synchrotron radiation excited soft x-ray emission and absorption spectroscopies. These spectroscopies allow the elementally resolved partial density of states of the valence and conduction bands to be measured. The x-ray absorption spectra indicate that the conduction band broadens considerably with increasing indium incorporation. The evolution of the band gap as a function of indium content derives primarily from this broadening of the conduction-band states. The emission spectra indicate that motion of the valence band makes a smaller contribution to the evolution of the band gap. This gap evolution differs from previous studies on the Al x Ga 1Ϫx N alloy system, which observed a linear valence-band shift through the series (0рxр1). For In x Ga 1Ϫx N the valence band exhibits a large shift between xϭ0 and xϭ0.1 with minimal movement thereafter. We also report evidence of In 4d-N 2p and Ga 3d-N 2p hybridization. Finally, the thermal stability of an In 0.11 Ga 0.89 N film was investigated. Both emission and absorption spectra were found to have a temperature-dependent shift in energy, but the overall definition of the spectra was unaltered even at annealing temperatures well beyond the growth temperature of the film.
Absorption and Emission of Hexagonal InN. Evidence of Narrow Fundamental Band Gap
physica status solidi (b), 2002
The physical properties of InN crystals are known rather poorly, since the existing growth techniques have not produced epitaxial layers of good quality . Even a key parameter of InN -the band gap E g -has not been firmly established so far. E g values of 1.8 eV to 2.1 eV have usually been estimated from the absorption spectra obtained on polycrystalline and nanocrystalline hexagonal InN . No data on the band-to-band photoluminescence (PL) of InN are available in the literature. Recently an improved growth technique has made it possible to obtain single-crystalline InN layers . Optical measurements on these InN layers have shown some strong differences from absorption data reported earlier . In the present work the electronic structure of singlecrystalline InN layers was carefully studied by means of optical absorption, PL, and photoluminescence excitation (PLE) spectroscopy as well as by ab initio calculations. Our results revealed for hexagonal InN a band gap of about 0.9 eV, which is much smaller than the values of 1.8 eV to 2.1 eV reported previously.
Physical Review B, 2002
The electronic structure of In x Ga 1Ϫx N alloys with (0рxр0.3) has been studied using synchrotron radiation excited soft x-ray emission and absorption spectroscopies. These spectroscopies allow the elementally resolved partial density of states of the valence and conduction bands to be measured. The x-ray absorption spectra indicate that the conduction band broadens considerably with increasing indium incorporation. The evolution of the band gap as a function of indium content derives primarily from this broadening of the conduction-band states. The emission spectra indicate that motion of the valence band makes a smaller contribution to the evolution of the band gap. This gap evolution differs from previous studies on the Al x Ga 1Ϫx N alloy system, which observed a linear valence-band shift through the series (0рxр1). For In x Ga 1Ϫx N the valence band exhibits a large shift between xϭ0 and xϭ0.1 with minimal movement thereafter. We also report evidence of In 4d -N 2p and Ga 3d -N 2p hybridization. Finally, the thermal stability of an In 0.11 Ga 0.89 N film was investigated. Both emission and absorption spectra were found to have a temperature-dependent shift in energy, but the overall definition of the spectra was unaltered even at annealing temperatures well beyond the growth temperature of the film.
Unusual properties of the fundamental band gap of InN
Applied Physics Letters, 2002
The optical properties of wurtzite-structured InN grown on sapphire substrates by molecular-beam epitaxy have been characterized by optical absorption, photoluminescence, and photomodulated reflectance techniques. These three characterization techniques show an energy gap for InN between 0.7 and 0.8 eV, much lower than the commonly accepted value of 1.9 eV. The photoluminescence peak energy is found to be sensitive to the free-electron concentration of the sample. The peak energy exhibits very weak hydrostatic pressure dependence, and a small, anomalous blueshift with increasing temperature.