Photocurrent measurements on GaAs1−xNx epilayers grown by metalorganic chemical vapor deposition

GaAs_1−xN_x epilayers were grown on a GaAs(0 0 1) substrate by metalorganic chemical vapor deposition. Composition was determined by high resolution X-ray diffraction. Band gap was measured from 77 to 400 K by using photocurrent measurements. The photocurrent spectra show clear near-band-edge peak and their peak energies drastically decrease with increasing nitrogen composition due to band gap bowing in the GaAs_1−xN_x epilayers. Those red shifts were particularly notable for low nitrogen compositions. However, the shifts tended to saturate when the nitrogen composition become higher than 0.98%. When the nitrogen composition is in the range 1.68–3.11%, the measured temperature dependence of the energy band gap was nicely fitted. However, the properties for the nitrogen composition range 0.31–0.98% could not be fitted with a single fitting model. This result indicates that the bowing parameter reaches 25.39 eV for low nitrogen incorporation (x=0.31%), and decreases with increasing nitrogen composition.     

Spectroscopic ellipsometry studies of reactively sputtered nitrogen-rich GaAsN films

Nitrogen-rich GaAsN thin films have been deposited at 500 °C by reactive rf sputtering of GaAs target in argon-nitrogen atmosphere. The arsenic content of the films was varied by changing the nitrogen percentage in the sputtering atmosphere and the As/Ga ratio in the films was estimated by X-ray fluorescence measurements. Spectroscopic ellipsometry measurements have been carried out on these films and the measured ellispometric spectra were fitted with theoretical spectra generated by using suitable model sample structures. From the best fit parameters of the dispersion model, band-gap values and variation of refractive index and extinction coefficient as a function of wavelength have been obtained for films deposited with different percentages of nitrogen in the sputtering atmosphere. The films deposited with 12% to 100% nitrogen in the sputtering atmosphere, which are of hexagonal GaN, exhibit GaN-like optical properties, though effects due to excess arsenic in amorphous phase are seen in the films deposited with less than 40% nitrogen. The films deposited with 5% to 12% nitrogen in sputtering atmosphere are dominantly polycrystalline GaAs_xN_1−x (x ≈ 0.01 to 0.08) and exhibit variations in optical parameters, which are consistent with their structure and composition. The films deposited with less than 5% nitrogen in sputtering atmosphere are arsenic-rich and amorphous.     

Technology and characterisation of GaAsN/GaAs heterostructures for photodetector applications

The nitrogen-containing conventional A^IIIB^V semiconductor alloys, so-called diluted nitrides (A^IIIB^V-N), have been extensively studied recently. Unusual properties of these materials make them very promising for applications in lasers and very efficient multijunction solar cells. This work presents the technology and properties of undoped GaAs_1-xN_x/GaAs heterostructures used as active regions in the construction of metal-semiconductor-metal (MSM) photodetectors. The atmospheric pressure metal organic vapour phase epitaxy (APMOVPE) was applied for growing MSM test structures. Their structural and optical properties were examined using high resolution X-ray diffraction (HRXRD), photoluminescence (PL), and photoreflectance spectroscopy (PR). Chemical wet etching was applied for forming an active region and a multifinger Schottky metallization was used as MSM contacts. Dark and illuminated current-voltage characteristics were measured. Based on the obtained results, the main detector parameters as responsivity and spectral response were estimated     

Synthesis and properties of N3 and CN delivery compounds and related precursors for nitride and ceramic fabrication

The simple azido and cyano compounds Cl₂AsN₃, Br₂AsN₃, (C₆H₅)SiH₂N₃, (C₆H₅)SiH₂CN and p‐(tolyl)SiH₂CN have been prepared for the first time by metathesis reactions involving the corresponding halides and NaN₃, LiN₃ and LiCN. These compounds represent a highly reactive and efficient family of delivery reagents for the preparation of N₃ and CN molecular precursors to bulk ceramics and nitride thin films. They are isolated as low volatility liquids and characterized by spectroscopic methods and chemical analysis. Ab initio simulations were used to elucidate the structural and vibrational properties of the simpler, fully inorganic Cl₂AsN₃ and Br₂AsN₃ species. This theoretical treatment was extended to include the hypothetical H₂AsN₃ and HClAsN₃ derivatives which are particularly desirable as single‐source low‐temperature As? N sources for the formation of highly sought after, metastable GaAs_1?xN_x materials for solar cell applications. The practical utility of the title molecules is also demonstrated by synthesizing several representative compounds of B, Be, Ga and Al, which are of interest for the development of open frameworks, optoelectronic nitrides and refractory B? C? N hybrids. The cyanide derivatives (C₆H₅)SiH₂CN and p‐(tolyl)SiH₂CN react readily with Be and B halides to yield crystalline Be(CN)₂ and amorphous B? C? N. The latter is crystallized upon heating to form graphite‐like polymorphs with homogeneous nanoscale morphologies. The azide derivatives Cl₂AsN₃, Br₂AsN₃ and (C₆H₅)SiH₂N₃ react readily with GaBr₃, GaCl₃ and BBr₃ to produce high yields of the previously reported Br₂GaN₃, Cl₂GaN₃ and Br₂BN₃, respectively. The latter is shown to possess a trimeric molecular structure in which the α‐nitrogen of the azide group bridges the boron atoms to form cyclohexane‐like B₃N₃ rings. Copyright © 2008 John Wiley & Sons, Ltd.     

GaAsN/GaAs量子阱在1 MeV电子束辐照下的退化规律

为研究GaAsN/GaAs量子阱在电子束辐照下的退化规律与机制,对GaAsN/GaAs量子阱进行了不同注量(1×1015,1×1016 e/cm2)1 MeV电子束辐照和辐照后不同温度退火(650,750,850℃)试验,并结合Mulassis仿真和GaAs能带模型图对其分析讨论。结果表明,随着电子注量的增加,GaAsN/GaAs量子阱光学性能急剧降低,注量为1×1015 e/cm2和1×1016 e/cm2的电子束辐照后,GaAsN/GaAs量子阱PL强度分别衰减为初始值的85%和29%。GaAsN/GaAs量子阱电子辐照后650℃退火5 min,样品PL强度恢复到初始值,材料带隙没有发生变化。GaAsN/GaAs量子阱辐照后750℃和850℃各退火5 min后,样品PL强度随退火温度的升高不断减小,同时N原子外扩散使得样品带隙发生约4 nm蓝移。退火温度升高没有造成带隙更大的蓝移,这是由于进一步的温度升高产生了新的N—As间隙缺陷,抑制了N原子外扩散,同时导致GaAsN/GaAs量子阱光学性能退化。     

Effect of electron and proton irradiation on recombination centers in GaAsN grown by chemical beam epitaxy

Deep level transient spectroscopy (DLTS) was deployed to study the evolution, upon electron irradiation and hydrogenation of GaAsN grown by chemical beam epitaxy, of the main nitrogen-related nonradiative recombination center (E1), localized at 0.33 eV below the bottom edge of the conduction band of the alloy. On one hand, the electron irradiation was found to enhance the density of E1 depending on the fluence dose. On the other hand, the hydrogenation was found to passivate completely E1. Furthermore, two new lattice defects were only observed in hydrogenated GaAsN films and were suggested to be in relationship with the origin of E1. The first defect was an electron trap at average thermal activation energy of 0.41 eV below the CBM of GaAsN and was identified to be the EL5-type native defect in GaAs, originating from interstitial arsenic (As_i). The second energy level was a hole trap, newly observed at average thermal activation energy of 0.11 eV above the valence band maximum of the alloy and its origin was tentatively suggested to be in relationship with the monohydrogen–nitrogen (N–H) complex. As the possible origin of E1 was tentatively associated with the split interstitial formed from one N atom and one As atom in single V-site [(N–As)_As], we strongly suggested that the new hole trap took place after the dissociation of E1 and the formation of N–H complex.     

Recent developments in metastable dilute-N III–V semiconductors

Metastable III–N–V semiconductors are a subgroup of a recently discovered new class of III–V and II–VI semiconductor alloys. Band gap engineering is achieved in these alloys by incorporating into a semiconductor host (e.g. GaAs) small amounts of an isoelectronic impurity (e.g. N) whose electronic levels are resonant with the host conduction band. Due to the large differences in size and electronegativity between the impurity and the host anion it substitutes, the band structure of the host is strongly perturbed and modified. The band structure formation of these alloys is totally different from that of conventional amalgamation-type semiconductor alloys such as (Al,Ga)As etc. Exemplarily, this review focuses on Ga(N,As) and (Ga,In)(N,As), which are currently the most prominent III–N–V alloys due to their application in optoelectronic devices. The review addresses electronic structure investigations ranging from bulk epitaxial layers to laser device structures. In particular, the band information process and the band structure of Ga(N,As) are described. Consequences such as the strong correlation between local N environment and global band gap, the metastability of quaternary (Ga,In)(N,As), and strong disorder and localization effects are discussed. Possible ways of parameterizing the band structure in a k·P-like fashion accounting for the effects of nitrogen are presented and employed to describe the electronic states of (Ga,In)(N,As)-based quantum wells. Furthermore, it is shown how (Ga,In)(N,As)/GaAs quantum wells in the active region of vertical-cavity surface-emitting laser structures can be characterized non-invasively.     

Double carriers pulse DLTS for the characterization of electron-hole recombination process in GaAsN grown by chemical beam epitaxy

A nitrogen-related electron trap (E1), located approximately 0.33 eV from the conduction band minimum of GaAsN grown by chemical beam epitaxy, was confirmed by investigating the dependence of its density with N concentration. This level exhibits a high capture cross section compared with that of native defects in GaAs. Its density increases significantly with N concentration, persists following post-thermal annealing, and was found to be quasi-uniformly distributed. These results indicate that E1 is a stable defect that is formed during growth to compensate for the tensile strain caused by N. Furthermore, E1 was confirmed to act as a recombination center by comparing its activation energy with that of the recombination current in the depletion region of the alloy. However, this technique cannot characterize the electron−hole (e-h) recombination process. For that, double carrier pulse deep level transient spectroscopy is used to confirm the non-radiative e-h recombination process through E1, to estimate the capture cross section of holes, and to evaluate the energy of multi-phonon emission. Furthermore, a configuration coordinate diagram is modeled based on the physical parameters of E1.     

Optical properties of GaInNAsSb/GaAs/GaAs1−xNx (x ≈ 10%) saturable absorber quantum wells

We study the effect of the GaAsN narrow QWs on the optical properties of the GaInNAsSb/GaAs QWs using photoluminescence spectroscopy. A drastic effect of the N-rich layers on the QW photoluminesecnec (PL) intensity was observed with a strong influence of the spacer thickness. In the PL spectra a broad band caused by excitonic transitions related with N-related clusters in GaAs barriers is found. Based on calculations from experimental data, we have identified the low QW peak energy to the E₁-H₁ transition using the shear deformation potentials report Δp/p = 0.24.