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.     

Isothermal capacitance transient spectroscopy (ICTS) study for midgap levels in Hb-GaAs by rapid thermal annealing

We studied the midgap levels by using isothermal capacitance transient spectroscopy (ICTS) in Hb-GaAs which had been processed by rapid thermal annealing (RTA). As the annealing time at 850 °C increased, the EL2 trap (E _c–0.81 eV) was transformed to the EX2 trap (E _c–0.73 eV) and eventually to the EX1 trap (E _c–0.87 eV). The diffusivity of the EL2 trap obtained from the experimental result of the heat treatment was about 1.02·10^–8cm²/s at 850 °C. This result indicate that the EL2 trap contains an interstitial arsenic atom. The result of the transformation to the EX1 and EX2 traps suggests that, when the EL2 trap is V_AsAS_iV_GaAs_Ga, the EX2 trap may be V_AsV_GaAs_Ga, which As_i is diffused out during a thermal annealing.     

Electronic structure of GaxIn1-xAsySb1-y quaternary alloy by recursion method

Summary  This work reports the electronic structure of GaInAsSb quaternary alloy by recursion method. A five-orbital sp₃s^* per atom model was used in the tight-binding representation of the Hamiltonian. The local density of states (LDOS), integrated density of states (IDOS) and structural energy (ST.E) were calculated for Ga, In, As and Sb sites in Ga_0.5 In_0.5 As_0.5 Sb_0.5 and GaInAsSb lattice matched to GaAs and the same alloy lattice matched to GaSb. There are 216 atoms in our cluster arranged in a zincblend structure. The results are in good agreement with available information about the alloy.     

Mutual passivation of electrically active and isovalent impurities in dilute nitrides

Using first-principles calculations we investigate the mutual passivation of shallow donor Si and isovalent N in dilute GaAsN alloys. Instead of the recently proposed pairing of Si and N on adjacent substitutional sites (Si(Ga)-N(As)) [K. M. Yu et al., Nat. Mater. 1, 185 (2002); J. Li et al., Phys. Rev. Lett. 96, 035505 (2006)] we find that N changes the behavior of Si in dilute nitride alloys in a more dramatic way. N and Si combine into a deep-acceptor split interstitial, where Si and N share an As site [(Si-N) (As)], with a significantly lower formation energy than that of the Si(Ga)-N(As) pair in n-type GaAs and dilute GaAsN alloys. The formation of (Si-N)(As) explains the GaAs band-gap recovery and the appearance of a photoluminescence peak at approximately 0.8 eV. This model can also be extended to Ge-doped GaAsN alloys, and correctly predicts the absence of mutual passivation in the case of column-VI dopants.     

Deep level transient spectroscopy investigation of deep levels in CdS/CdTe thin film solar cells with Te:Cu back contact

Deep levels in Cds/CdTe thin film solar cells have a potent influence on the electrical property of these devices. As an essential layer in the solar cell device structure, back contact is believed to induce some deep defects in the CdTe thin film. With the help of deep level transient spectroscopy (DLTS), we study the deep levels in CdS/CdTe thin film solar cells with Te:Cu back contact. One hole trap and one electron trap are observed. The hole trap H1, localized at E_v+0.128~eV, originates from the vacancy of Cd (V_Cd. The electron trap E1, found at E_c-0.178~eV, is considered to be correlated with the interstitial Cu_i⁼ in CdTe.     

Prediction of enhanced ferromagnetism in (Ga,Mn)As by intrinsic defect manipulation

In the diluted magnetic semiconductor (Ga,Mn)As the excess of As incorporated as As antisites (As_Ga) is responsible for the hole compensation. The As_Ga defect can be transformed into a As interstitial–Ga vacancy pair (As_i–V_Ga) upon illumination. In this paper we study the effects of such a transition on the ferromagnetism of (Ga,Mn)As using density functional theory within the local spin density approximation. We find that the ferromagnetic order in (Ga,Mn)As is strongly enhanced if As_Ga are transformed into As_i–V_Ga pairs, since the hole compensation is reduced. This suggests a valuable way to tune the carrier concentration and hence the T_c in (Ga,Mn)As, without changing the Mn concentration nor the microscopic configuration of the Mn ions.     

Space-charge-limited-trap-limited-currents in anthracene crystals

Space-charge-limited-trap-limited hole currents in anthracene crystals are interpreted in terms of a trap distribution which starts at a discrete trap level at 0·6–0·8 eV and in which the trap density falls off exponentially with energy relative to this level. It is suggested that exponential hole trap distributions are produced by physical perturbations of the crystal lattice introduced by the same impurities which give rise to the discrete hole trap level at 0·6–0·8 eV (revealed by thermally stimulated current studies). The results indicate that a perturbed molecule is introduced for every 10,000 impurity molecules and the total number of perturbed molecules is constant at 10¹⁷ m^?3 for melt-grown and vapor-grown crystals. The parameter kT_c varies from crystal to crystal, indicating that the relative contributions of highly perturbed and slightly perturbed molecules is influenced by crystal growth conditions.     

有机铬富勒烯衍生物的激发态与光限幅特性

应用倍频ｎｓ／ｐｓＮｄ：ＹＡＧ脉冲激光系统,在波长为５３２ｎｍ,脉冲宽度为２１ｐｓ的条件下,研究了新型有机铬富勒烯衍生物的激发态吸收与光限幅特性,其光限幅特性优于富勒烯甲苯溶液;并应用单重态激发态吸收理论对实验结果进行了分析,实验结果与理论结果基本一致。     

The aluminum arsenides Al<Subscript>m</Subscript>As<Subscript>n</Subscript> (m + n = 2–5) and their anions: Structures,electron affinities and vibrational frequencies

Geometries, electronic states and electron affinities of Al_mAs_n and Al_mAs _n (m+n=2–5) clusters have been examined using four hybrid and pure density functional theory (DFT) methods. Structural optimization and frequency analyses are performed using a 6-311+G(2df) one-particle basis set. The geometries are fully optimized with each DFT method independently. The three types of energy separations reported in this work are the adiabatic electron affinity (EA_ad), the vertical electron affinity (EA_vert), and the vertical detachment energy (VDE). The calculation results show that the singlet structures have higher symmetry than that of doublet structures. The best functional for predicting molecular structures was found to be BLYP, while other functionals generally underestimated bond lengths. The largest adiabatic electron affinity, vertical electron affinity and vertical detachment energy, obtained at the 6-311+G(2df)/BP86 level of theory, are 2.20, 2.04 and 2.27 eV (AlAs), 2.13, 1.94 and 2.38 eV (AlAs₂), 2.44, 2.39 and 2.47 eV (Al₂As), 2.09, 1.80 and 2.53 eV (Al₂As₂), 2.01, 1.57 and 2.36 eV (AlAs₃), 2.32, 2.11 and 2.55 eV (Al₂As₃), 2.40, 1.45 and 3.26 eV (AlAs₄), 1.94, 1.90 and 2.07 eV (Al₄As), respectively. However, the BHLYP method gives the largest values for EA_ad and EA_vert of Al₃As and EA_ad of Al₃As₂, respectively. For the vibrational frequencies of the Al_nAs_m series, the B3LYP method produces good predictions with the average error only about 10 cm^-1 from available experimental and theoretical values. The other three functionals overestimate or underestimate the vibrational frequencies, with the worst predictions given by the BHLYP method.     

Electron and hole injection in metal-oxide-nitride-oxide-silicon structures

The kinetics of electron and hole accumulation in metal-oxide-nitride-oxide-semiconductor structures is studied. Experimental data are compared with a theoretical model that takes into account tunnel injection, electron and hole capture by traps in amorphous silicon nitride SiN_x, and trap ionization. Agreement between experimental and calculated data is obtained for the bandgap width E _g = 8.0 eV of amorphous SiO₂, which corresponds to the barrier for holes Φ_h = 3.8 eV at the Si/SiO₂ interface. The tunneling effective masses for holes in SiO₂ and SiN_x are estimated at m _h ^* ≈ (0.4–0.5)m ₀. The parameters of electron and hole traps in SiN_x are determined within the phonon-coupled trap model: the optical energy W _opt = 2.6 eV and the thermal energy W _T = 1.3 eV.     

A study of deformation-produced deep levels inn-GaAs using deep level transient capacitance spectroscopy

Deformation-produced deep levels, both of electron and hole traps, have been studied using deep level transient capacitance spectroscopy (DLTS) for an undopedn-type GaAs (HB grown) compressed at 440°C. Concentrations of two grown-in electron trap levels (E _c −0.65eV andE _c −0.74eV) and one grown-in hole trap level (E _v +∼0.4eV) increase with plastic deformation, while that of a grown-in electron trap level (E _c −∼0.3eV) decreases in an early stage of deformation. While no new peak appeared in the electron trap DLTS spectrum after plastic deformation, in the hole trap DLTS spectrum a broad spectrum, seemingly composed of many peaks, newly appeared in a middle temperature range, which may be attributed to electronic energy levels of dislocations with various characters.     

Deep level transient spectroscopy in Hg1−xCdxTe

We report the application of Deep Level Transient Spectroscopy (DLTS) in Hg_1-xCd_xTe, demonstrating for the first time the utilization of DLTS techniques in a narrow band-gap semiconductor, E_g < 0.40 eV. DLTS measurements performed on an n⁺-p diode with E_g (x=0.21, T=30 K) =0.096 eV have identified an electron trap with an energy of E_v + 0.043 eV and a hole trap at E_v + 0.035 eV. Measurements of trap densities, capture cross sections, and the close proximity of the electron and hole trap locations within the band-gap suggest that DLTS may be observing both the electron and hole capture at a single Shockley-Read recombination center. The trapping parameters measured by DLTS predict minority carrier lifetime versus temperature data to be comparable with the experimentally measured values.     

Evidence for two energy levels associated with EL2 trap in GaAs

By photocapacitance technique, applied to n-type LEC-grown GaAs, two energy levels:E _v +0.45 eV andE _c –0.75 eV are identified, for the first time, as being associated with the EL2 trap. As follows from the analysis of photo-EPR results on highly resistive GaAs crystals, the same energy levels can be attributed to the arsenic antisite defect, As_GA. In view of these findings, it is argued that the occupied EL2 level corresponds to the neutral charge state of As_Ga defect.     

The comparison of Ag–As33S67 films prepared by thermal evaporation (TE), spin-coating (SC) and a pulsed laser deposition (PLD)

Chalcogenide thin films could be prepared by many experimental methods resulting in some differences in structure and physicochemical properties of prepared films. In this work, the As₃₃S₆₇ amorphous films were prepared by three different preparation techniques: vacuum thermal evaporation (TE), pulsed laser deposition (PLD) and spin-coating (SC). A silver film was deposited on the top of the As₃₃S₆₇ films and photodoped.The X-ray diffraction analysis showed significant differences in arrangement between bulk glass and thin films and also among films themselves. The Raman spectroscopy showed that the Raman spectra of PLD film and bulk glass are almost similar. On the other hand, TE films contain higher amount of homopolar bonds As–As and S–S. The value of refractive index of As₃₃S₆₇ bulk glass was 2.31. All prepared films have lower index of refraction contrary to bulk glass, i.e. TE∼2.27, PLD∼2.20 and SC∼1.90. The increase of refractive index with silver concentration is shown either. The optical bandgap of undoped As–S prepared films was different: TE∼2.42 eV, PLD∼2.45 eV and SC∼2.54 eV.     

Characterization of GaAs/AlxGa1-xAs heterointerface defects by means of capacitive measurememts

x Ga_1-xAs heterojunctions grown by liquid-phase epitaxy. Interface states with hiqh concentration, N_t=3×10¹¹ cm^-2 and energy level E_c-E_t=0.14 eV distributed in a box 150 Å wide at the heterointerface and acting as electron traps are observed. The possible origin could be the isolated arsenic vacancy V_As in n-GaAs. Received: 25 April 1996/Accepted: 22 January 1997     

Competition of N-passivation and Te-passivation in hydrogenation of Te-doped (Ga,In)(N,As)

(Ga,In)(N,As) lattice matched to GaAs with a band gap of 1 eV is employed as active material in high-efficiency III–V solar cells. Te-doped Ga_0.934In_0.066N_0.023As_0.977 layers were grown by metal-organic vapor-phase epitaxy on (1 0 0) GaAs. The samples were highly doped n-type with carrier concentrations ranging from about 10¹⁷–10¹⁹ cm⁻³. Pieces of the samples were hydrogenated with H-doses of 10¹⁸ ion/cm². The optical and electrical properties of the samples before and after hydrogenation were studied by low-temperature photoluminescence and magnetotransport. In undoped samples hydrogen is known to form N–H complexes which strongly reduce the local perturbation of the lattice due to nitrogen and thus reverse the N-induced global changes of the band structure. Combined analysis of photoluminescence and transport measurements on Te-doped samples, however, indicates a competition between N–H formation and passivation of the Te donor favoring the latter. Hardly any band structure changes due to hydrogenation are observed in these Te-doped samples, instead a strong reduction of the free-carrier concentration is observed after hydrogenation.     

New photoluminescence defect spectra in silicon irradiated at 100 K: Observation of interstitial carbon?

We report photoluminescence spectra of defects in irradiated silicon which are stable below room temperature. No-phonon lines (STI)⁰ at ≈ 856 meV, ST2 at ≈ 1115 meV, and ST3 at ≈ 1126 meV are observed along with a broad emission band extending from 0.7 to 1 eV. The ST1 defect studied in detail is a deep hole trap at ≈ E_v + 0.25 eV, which in addition can bind an electron loosely. Piezospectroscopy shows that the defect is essentially <100 > axial symmetric with slight distortion to C_1h. The absence of Zeeman splittings confirms the deep hole binding in an axially symmetric potential. The independence of dopants, the annealing behaviour, and comparison to EPR and IR active defects suggest a correlation of the ST1 defect with interstitial carbon.     

注硅半绝缘GaAs的深能级

用深能级瞬态谱(DLTS)详细研究了硅离子注入Liquid-encapsulated Czochralski(缩写为LEC)半绝缘GaAs的深中心。结果表明,在注硅并经高温退火的有源区中观测到4个多子(电子)陷阱,E₀₁,E₀₂,E₀₃和E₀₄。它们的电子表观激活能分别为0.298,0.341,0.555和0.821eV。其中E₀₄与EL2有关,但不是EL2缺陷。E₀₄的电子 关键词：     

双异质结AlxGa1-xAs/GaAs发光管中与氧有关能级的测量

用DLTS和单次脉冲瞬态电容技术研究了液相外延生长的双异质结AlxGa1-xAs/GaAs发光管,掺Si的n-Al0.05Ga0.95As有源层中的深能级。着重分析了一个与氧有关的电子陷阱,其发射激活能为EC-ED=0.29eV。我们发现该电子陷阱随正向注入脉冲宽度tp的增加DLTS峰向低温移动,即在确定的温度下发射率随tp的增加而增加。用DLTS首次测得该能级的俘获瞬态谱,发现俘获峰随反向撤空脉冲宽度tR的增加向低温端移动,即在确定的温度下俘获率随tR的增加而增加,并且俘获激活能从△Eσ=0.28eV变化到0.26eV,用位形坐标图讨论了引起变化的原因。     

Investigation of persistent photoconductivity in Si-dopedn-Al x Ga1−x as grown by molecular beam epitaxy

The persistent photoconductivity effect in Si-dopedn-Al _x Ga_1?x As layers grown by molecular beam epitaxy on (100)GaAs substrates has been investigated by detailed Halleffect and capacitance measurements at 10–300 K. In the alloy composition range 0.25<x <0.40 the electrical properties ofn-Al _x Ga_1?x As are governed by a deep electron trap having an emission barrier of 0.34–0.40 eV (depending on the doping concentration), as determined by admittance measurements. The concentration of deep electron traps, deduced from low-temperature capacitance measurements, is found to coincide with the amount of persistent photoconductivity observed in the material. Consequently, the earlier proposed population of two-dimensional subbands at the Al _x Ga_1?x As/GaAs-substrate hetero-interface, i.e. charge separation bymacroscopic barriers, can not account for the measured high overall number of persistent photoexcited carriers. Instead, the vanishing small capture rates of photoexcited electrons result frommicroscopic capture barriers. The dominant deep electron trap, which we attribute to deep donor-type (DX) centers, is found to be homogeneously distributed throughout the Al _x Ga_1?x As layer depth. From our Hall effect measurements a trap depth of 0.05–0.12 eV (depending on the doping concentration) below the conduction band is derived. The capture barrier is thus in the order of 0.30 eV. This value is in excellent agreement with data obtained from liquid phase epitaxially grown Si-dopedn-Al _x Ga_1?x As.