Study of grown-in defects and effect of thermal annealing in Al0.3Ga0.7As and GaAs LPE layers

Studies of the grown-in deep-level defects in the undoped n-Al_xGa_1-xAs (x = 0.3) and GaAs epitaxial layers prepared by the liquid phase epitaxy (LPE) techniques have been made, using DLTS, I-V and C-V measurements. The effect of 300 °C thermal annealing on the grown-in defects was investigated as a function of annealing time. The results showed that significant reduction in these grown-in defects can be achieved via low temperature thermal annealing process. The main electron and hole traps observed in the Al_0.3Ga_0.7As LPE layer were due to the E_c-0.31 eV and E_v+0.18 eV level, respectively, while for the GaAs LPE layer, the electron traps were due to the E_c-0.42 and 0.60 eV levels, and the hole traps were due to E_v+0.40 and 0.71 eV levels. Research supported in part by the Air Force Wright Aeronautical Laboratories, Aeropropulsion Lab., Wright Patterson Air Force Base, Ohio, subcontract through SCEEE, contract F33615-81-C-2011, task-4, and in part by AFOSR grant no. 81-0187.     

Origin of photoluminescence from Er3+ centers in erbium doped GaAs and Al0.4Ga0.6 As grown by MBE

Sharp erbium-related intra-4f shell luminescence from Er doped GaAs and Al_0.4Ga_0.6 As epitaxial layers grown by molecular beam epitaxy (MBE) is presented. The emission arising from the two Er³⁺ excited states,⁴I_13/2 and⁴I_11/2 are studied. We have observed, by means of heat treatment under differentambients such as As, Ga and Al over pressure, that the optically active Er³⁺ preferentially occupies a Column III lattice site or Column III related defects. The photoluminescence results of co-doping Al_0.4Ga_0.6As:Er with Si and Be by MBE is also reported for the first time. A strong single 1.54 μm spontaneous emission line is achieved by co-doping with Be (≈1×10¹⁸ cm⁻³). This improvement is a result of successfully eliminating or suppressing the other transitions without sacrificing the 1.54 μm emission intensity or linewidth.     

Dislocation-Induced deep level states in In0.08Ga0.92As/GaAs heterostructures

We have performed luminescence experiments on In_0.08Ga_0.92As/GaAs heterointerfaces to explore the energy distribution of deep level states in the bandgap for two cases: (1) unrelaxed, pseudomorphic In_0.08Ga_0.92As films (200Å thick), which have few if any dislocations at the interface, and (2) partially relaxed In_0.08Ga_0.92As films (1000Å thick) which are expected to have a substantial interfacial dislocation density. A combined photoluminescence and cathodoluminescence technique is used which allows us to profile the sample luminescence through the buried interface region. Our results show the existence of deep level luminescent features characteristic of the GaAs substrate and features common to In_0.08Ga_0.92As and GaAs, as well as the existence of a deep level feature near 1 eV photon energy which undergoes a shift in energy depending upon the degree of strain relaxation in the In_0.08Ga_0.92As film. In addition, a deep level feature near 0.83 eV becomes prominent only in In_0.08Ga_0.92As films which have relaxed, and thus contain misfit dislocations at the interface. These deep level differences may be due to bandgap states associated with the intrinsic dislocation structure, impurities segregated at the dislocation, or bulk point defects, or threading dislocations generated during the strain relaxation. Previous work has determined that a deep level state 0.7 eV above the valence band edge would account for the electrical behavior of relaxed In_0.08Ga_0.92As/GaAs interfaces, which is in good agreement with the range of deep level transitions near 0.8 eV photon energy which we observe. These measurements suggest that photo- and cathodoluminescence measurements of deep level emission in these III-V semiconductors can provide a useful indicator of electrically active defect densities associated with misfit dislocations.     

Diffusion of zinc into gaas layers grown by molecular beam epitaxy at low substrate temperatures

We report the diffusion of zinc into low temperature (LT) GaAs grown by MBE at 200° C, the problems associated with using a silicon nitride film directly deposited on the LT GaAs as a Zn diffusion mask, and several schemes to avoid the problems. The Zn diffusion coefficient is measured (sealed-ampoule technique) to be about one order of magnitude higher in the LT GaAs than in normal GaAs, attributed to a large quantity of defects including arsenic antisites (As_Ga) in the LT GaAs. The effectiveness of silicon nitride as a Zn diffusion mask depends if the mask is deposited directly on the LT GaAs. The failure of the nitride directly deposited on the LT GaAs to stop the Zn is attributed to arsenic atoms outdiffusing from the As-rich LT GaAs (about 1 at. % excess As) into the nitride. Several structures are introduced including a 100-Å thick GaAs layer on the LT GaAs that are effective in preserving the diffusion mask properties of the silicon nitride.     

Analysis of 14nm technology node In0.53Ga0.47As nFinFET integrated with In0.52Al0.48As cap layer for high-speed circuits

CMOS (Complementary Metal-oxide-semiconductor) based high-speed applications in the sub-14 nm technology node using InGaAs Fin field-effect-transistors (FinFETs) confront with inevitable effect in form of interface traps upon integration of dielectric layer with InGaAs material. In this work, we have explored the impact of the traps on short channel effects (SCEs) and a technique of abating the effect of interface traps by introducing In_0.52Al0.₄₈As cap layer. Proposed work reforms the device by varying the cap layer thickness (Tcap), doping concentrations of cap layer and underlap region. The effect of traps on intrinsic delay, work function variation and SCEs was investigated to assess the trend on devices with In_0.52Al_0.48As cap layer. It has been observed that introduction of Tcap improves SCEs and helps to mitigate the effect of interface traps. SCEs can be additionally diminished by presenting underlap fin length at the cost of higher delay. The experimental results show the value of subthreshold swing = 149.54 mV/decade, drain-induced barrier lowering = 38.5 mV V^?1 and delay = 1.1 ps for T_cap = 4 nm without underlap fin length structure for traps concentration of 10¹² cm^?2eV^?1. Thus, significant improvement has been seen in SCEs and delay performance in FinFET structure with cap layer.     

掺杂GaAs/Al0.3Ga0.7As超晶格的光致发光特性分析

在室温下,通过光致发光实验研究了用MBE生长的GaAs/Al0.3Ga0.7As超晶格材料的光致发光特性,对测得的发光峰进行了指认.理论计算和实验结果符合很好.     

OMVPE growth of In0.53Ga0.47As on InP using tertiarybutylarsine

We have successfully grown bulk In_0.53Ga_0.47As on InP using tertiarybutylarsine (TBA), trimethylindium and trimethylgallium. The growth temperature was 602° and the V/III ratio ranged from 19 to 38. Net carrier concentrations were 2 – 4 × 10¹⁵ cm^-3, n-type, with a peak 77 K mobility of 68,000 cm²/V. sec. Increasing compensation was observed in In_0.53Ga_0.47As grown at higher V/III ratios. PL spectra taken at 5 K revealed strong near bandgap emission at 0.81 eV—with the best sample having a FWHM of 2.5 meV. At lower energies, donor-acceptor pair transitions were evident. Strong and sharp 5 K PL emission was observed from InP/In_0.53Ga_0.47As/InP quantum wells grown with TBA.     

The profile of temperature and voltage dependent series resistance and the interface states in (Ni/Au)/Al0.3Ga0.7N/AlN/GaN heterostructures

The temperature dependence of capacitance-voltage (C-V) and the conductance-voltage (G/w-V) characteristics of (Ni/Au)/Al_0.3Ga_0.7N/AlN/GaN heterostructures were investigated by considering the effect of series resistance (R_s) and interface states N_ss in a wide temperature range (79-395 K). Our experimental results show that both R_s and N_ss were found to be strongly functional with temperature and bias voltage. Therefore, they affect the (C-V) and (G/w-V) characteristics. The values of capacitance give two peaks at high temperatures, and a crossing at a certain bias voltage point (∼3.5 V). The first capacitance peaks are located in the forward bias region (∼0.1 V) at a low temperature. However, from 295 K the second capacitance peaks appear and then shift towards the reverse bias region that is located at ∼−4.5 V with increasing temperature. Such behavior, as demonstrated by these anomalous peaks, can be attributed to the thermal restructuring and reordering of the interface states. The capacitance (C_m) and conductance (G/w-V) values that were measured under both reverse and forward bias were corrected for the effect of series resistance in order to obtain the real diode capacitance and conductance. The density of N_ss, depending on the temperature, was determined from the (C-V) and (G/w-V) data using the Hill-Coleman Method.     

Properties of Ge-doped GaAs and Alx Ga1−xAs,Sn-doped Alx Ga1−xAs and Si-Te-doped GaAs

In order to better understand the electrical and optical properties of GaAs and Al_xGa_1-x As used in making double heterojunction lasers, we have studied the Hall coefficient, resistivity and photoluminescence behavior of doped epitaxial samples of these materials. In particular, we report results on Ge-doped GaAs and Al_x Ga_1-x As, Sn-doped Al_xGa_1-x As and Si-Te-doped GaAs single crystal layers which were grown on GaAs substrates by the liquid phase epitaxial method. The effects of impurities in the solution on the carrier concentration, mobility, photoluminescence spectra and possible recombination processes in these layers are discussed.     

The behavior of unintentional impurities in Ga0.47 In0.53As grown by MBE

A number of factors contribute to the high n-type background carrier concentration (high 10¹⁵ to low 10¹⁶ cm⁻³) measured in MBE Ga_0.47In_0.53As lattice-matched to InP. The results of this study indicate that the outdiffusion of impurities from InP substrates into GalnAs epitaxial layers can account for as much as two-thirds of the background carrier concentration and can reduce mobilities by as much as 40%. These impurities and/or defects can be gettered at the surfaces of the InP by heat treatment and then removed by polishing. The GalnAs epitaxial layers grown on the heat-treated substrates have significantly improved electrical properties. Hall and SIMS measurements indicate that both donors and acceptors outdiffuse into the epitaxial layers during growth resulting in heavily compensated layers with reduced mobilities. The dominant donor species was identified by SIMS as Si, and the dominant acceptors as Fe, Cr and Mn.     

Electrical characterization of self-assembled In0.5Ga0.5As/GaAs quantum dots by deep level transient spectroscopy

We have investigated electron emission from self-assembled In_0.5Ga_0.5As/GaAs quantum dots (QDs) grown by molecular-beam epitaxy (MBE). Through detailed deep level transient spectroscopy comparisons between the QD sample and a reference sample, we determine that trap D, with an activation energy of 100 meV and an apparent capture cross section of 5.4×10⁻¹⁸ cm², is associated with an electron quantum level in the In_0.5Ga_0.5As/GaAs QDs. The other deep levels observed, M1, M3, M4, and M6, are common to GaAs grown by MBE.     

Fe and Ti implants in In0.52Al0.48As

Single (200 keV) and multiple energy Fe implants in n-type and Ti implants in p-type material were performed in In_0.52Al_0.48As at both room temperature and 200°C. For the Fe implants, the secondary ion mass spectrometry profiles showed a severe out-diffusion for all rapid thermal annealing schemes used, independent of the implantation temperature. The Fe implant peaks observed after annealing, at 0.8Rp, Rp+ΔRp and 2Rp (where Rp and ΔRp are range and straggle, respectively) depth locations in other In-based compounds like InP and InGaAs were not observed here. On the contrary, Ti implants showed only a slight in- and out-diffusion for both room temperature and 200°C implants as in the case of InP and InGaAs. The Rutherford backscattering measurements on the annealed samples implanted at 200°C showed a crystal quality similar to that of the virgin material. The resistivity of all the samples after annealing was higher than 10⁶ Ω-cm.     

High uniformity of Al0.3Ga0.7As/ln0.15Ga0.85As doped-channel structures grown by molecular beam epitaxy on 3″ GaAs substrates

Al_0.3Ga_0.7As/ln_0.15Ga_0.85As doped-channel structures were grown by molecular beam epitaxy on 3″ GaAs substrates. The uniformities of electrical and optical properties across a 3″ wafer were evaluated. A maximum 10% variation of sheet charge density and Hall mobility was achieved for this doped-channel structure. A1 μm long gate field-effect transistor (FET) built on this layer demonstrated a peak transconductance of 350 mS/mm with a current density of 470 mA/mm. Compared to the high electron mobility transistors, this doped-channel FET provides a higher current density and higher breakdown voltage, which is very suitable for high-power microwave device applications.     

Electron-concentration dependence of absorption and refraction in n-In0.53Ga0.47As near the band-edge

The optical constants of InGaAs were determined as a function of electron concentration in the range from 10¹⁵ to 2 × 10¹⁹ cm⁻³ by reflectance- and transmission-spectroscopy. A pronounced shift of the fundamental absorption edge toward shorter wavelengths with increasing doping concentration was found. The experimental results can be satisfactorily explained by band-filling and band-gap shrinkage.     

新型复合沟道Al0.3Ga0.7N/Al0.05Ga0.95N/GaN HEMT低相位噪声微波单片集成压控振荡器

设计并研制了一种新型复合沟道Al0.3Ga0.7N/Al0.05Ga0.95N/GaN HEMT(CC-HEMT)微波单片集成压控振荡器(VCO),且测试了电路的性能.CC-HEMT的栅长为1μm,栅宽为100μm.叉指金属-半导体-金属(MSM)变容二极管被设计用于调谐VCO频率.为提高螺旋电感的Q值,聚酰亚胺介质被插入在电感金属层与外延在蓝宝石上GaN层之间.当CC-HEMT的直流偏置为Vgs=-3V,Vds=6V,变容二极管的调谐电压从5.5V到8.5V时,VCO的频率变化从7.04GHz到7.29GHz,平均输出功率为10dBm,平均功率附加效率为10.4%.当加在变容二极管上电压为6.7V时,测得的相位噪声为-86.25dBc/Hz(在频偏100KHz时)和-108dB/Hz(在频偏1MHz时),这个结果也是整个调谐范围的平均值.据我们所知,这个相位噪声测试结果是文献报道中基于GaN HEMT单片VCO的最好结果.     

基于InP衬底的晶格失配In0.68Ga0.32As的MOCVD生长及其特性研究

采用MOCVD生长技术在InP衬底上成功实现了晶格失配的3μm In0.68 Ga0.32As薄膜生长.通过As组分的改变,利用张应变和压应变交替补偿的InAsxP1-x应变缓冲层结构来释放由于晶格失配所产生的应力,在InP衬底上得到了与In0.68Ga0.32 As晶格匹配的InAsxP1-x“虚拟”衬底,通过对缓冲层厚度的优化,使应力能够在“虚拟”衬底上完全豫弛.通过原子力显微镜(AFM)、高分辨XRD、透射电镜(TEM)和光致发光(PL)等测试分析表明,这种释放应力的方法能够有效提高In0.68 Ga0.32 As外延层的晶体质量.     

Comparative study on the influence of Al component at GaAlAs layer for GaAs/AlGaAs photocathode

We designed two transmission-mode GaAs/AlGaAs photocathodes with different AlxGa_1-xAs layers, one has an Al_xGa_1-xAs layer with the Al component ranging from 0.9 to 0, and the other has a fixed Al component 0.7. Using the first-principle method, we calculated the electronic structure and absorption spectrum of Al_xGa_1-xAs at x=0, 0.25, 0.5, 0.75 and 1, calculation results suggest that with the increase of the Al component, the band gap of Al_xGa_1-xAs increases. Then we activated the two samples, and obtained the spectral response curves and quantum efficiency curves; it is found that sample 1 has a better shortwave response and higher quantum efficiency at short wavelengths. Combined with the band structure diagram of the transmission-mode GaAs/AlGaAs photocathode and the fitted performance parameters, we analyze the phenomenon. It is found that the transmission-mode GaAs/AlGaAs photocathode with variable Al component and various doping structure can form a two-stage built-in electric field, which improves the probability of shortwave response photoelectrons escaping to the vacuum. In conclusion, such a structure reduces the influence of back-interface recombination, improves the shortwave response of the transmission-mode photocathode.     

Systematic optical and x-ray study of In x Ga1−x As on InP

We present a systematic study of In _x Ga_1−x As on InP grown by molecular beam epitaxy using the characterization techniques of Fourier transform photoluminescence, x-ray diffraction, micro-Raman spectroscopy, and photoreflectance spectroscopy. The four techniques were used to determine and correlate the fundamental parameters of band-gap energy, phonon frequency and composition. Comparing room temperature (293 K) PL and low temperature PL indicate the presence of a partially ionized acceptor with binding energy of about 13 meV in the unintentionally doped material. Double crystal x-ray diffraction (XRD) using a symmetric <400> and asymmetric <224> reflections was also employed. The use of two reflections gives precise lattice constants, composition, and extent of film relaxation. Micro-Raman spectroscopy was used to measure phonon frequencies in the In _x Ga_1−x As films and correlated to XRD composition. Room temperature photoreflectance (PR) was used to determine band-gap energy for both the low and intermediate field cases. Band gap energies determined at room temperature by PL and PR were in agreement within experimental error.     

Capacitance-voltage profiling and thermal evolution of the conduction band-offset of unstrained Ga0.47In0.53As/InP single quantum well

We report the results of capacitance-voltage (C-V) and Deep Level Transient Spectroscopy (DLTS) measurements performed upon a Ga_0.47In_0.53As/InP quantum well structure. At room temperature, a conduction-band offset ΔE_c=(200±10)meV and charge densities σ_I=±(3±1)*10¹¹ times the electronic charge per cm² have been measured from C-V experiments. At lower temperature (T≤150K) we have observed an important decrease of the band-offset, considerably larger than a pure thermal effect. We have shown that the explanation lies in the presence of a high concentration of deep traps located at the well-barrier interfaces. Two species A and B have been detected through DLTS experiments with activation energies E_tA=90 meV and E_tB=195 meV, respectively. The filling of these trap levels at low temperature lowers the band offset from 200 to 120 meV, owing to band repulsion effects.     

Properties of Zn-doped P-type In0.53Ga0.47as grown by vapor phase epitaxy (VPE) on InP substrates

Electrical properties of Zn-doped, p-type In_0.53Ga_0.47As grown by the vapor phase epitaxy (VPE) technique are presented. High (p ∼ 4.0 × 10¹⁹ cm⁻³) p-type doping and low resistivity (ρ ∼ 2.8 × 10⁻³ Ωsu−cm) was obtained. These propertie's are useful in the formation of ohmic contacts in laser diodes and photodiodes fabricated from the quaternary and ternary alloy systems. A calibration curve for the non-destructive determination of carrier concentration from photoluminescence linewidths has been obtained.