Zn在InP中低温扩散的研究

本文用Zn3P2源在闭管条件下研究了Zn在InP中的低温(520700℃)扩散。比较了用等温扩散和双温区扩散技术扩散后,样品的电学参数。结果表明:双温区扩散法可得到表面光亮,无损伤的高浓度表面层。该法已用于InGaAsP/InP双异质结发光管的制备工艺中,并制得了光功率1mW,串联电阻23的发光管。还讨论了Zn在InP中扩散时的行为,解释了低温(550℃)扩散过程中,等温扩散时出现的异常现象。     

On-line growth monitoring of InP-based device structures by reflectance anisotropy spectroscopy

Reflectance anisotropy spectroscopy (RAS) has been used to study the metalorganic vapor phase epitaxy growth process for Ga_xIn_1−xAs_yP_1−y/InP light emitting diodes. The sensitivity of RAS to morphology changes is demonstrated by InP growth on different InP:Fe substrates. RAS reveals not only development of dull surfaces but also detects initial temporary roughness of mirror-like layers. Based on the RAS results the substrate preparation was optimized. RAS spectra measured on n- and p-type InP and p-type GaInAsP during light emitting diodes production are suitable for finger-printing of the growth process. Spectra from InP:Si and InP:Zn layers show characteristic features near 4.3 eV which allow for assessment of doping level at growth temperature (640°C). Correlation of RAS spectra and transients during growth with the quaternary composition was achieved. A change in composition of only Δx=0.01, Δy=0.03 corresponding to a shift of photoluminescence-peak position by 16 nm was detectable in RAS spectra. The results demonstrate the high sensitivity and thus the suitability of RAS for on-line control during growth of device structures.     

The diffusion of Zn in GaAs at low temperature

The diffusion of Zn into GaAs at low temperature has been investigated. The experiments are carried out in an evacuated and sealed quartz ampoule using ZnAs₂ as the source of Zn. The relation among the junction depth (X _j), the time (t) and the temperature (T) of diffusion has been investigated. It is found that the sheet resistance (R _s) of diffusion layer increases asX _j decreases. The surface concentration (C _s) decreases as 1/T increases, and mobility (μ) decreases asC _s increases. TheC _s versus 1/X _j·R_s) are plotted, the results are thatC _s increases as 1/X _j ·R _s ) increases. This is a simple method for determiningC _s of the multiple GaAs/GaA1As epitaxial layer. The mechanism of Zn diffusion in GaAs and InP is discussed. This process has been applied to fabricate GaAs/GaAlAs double heterojunction light emitting diodes and an output power of 2—4mW is obtained, the series resistance is 3—5Q.     

Selective area LPE growth and open tube diffusion in InGaAs/InP

Techniques are described in which selective chemical etching, localised LPE growth and localised diffusion in In_0.53Ga_0.47As and InP were carried out. Spun-on silica films were employed as masks in these processes and its performance was found to be comparable with pyrolytic or rf deposited films. Localised LPE growth of In_0.53Ga_0.47As and in-situ etching enabled well-controlled islands of In_0.53Ga_0.47As embedded in InP to be produced. Orientation dependent growth rates were also identified. An open-tube diffusion technique based on an LPE growth system has been successfully used for diffusion of Zn into InP and In_0.53 Ga_0.47As from Sn solutions. A strong variation of diffusion depth in InP with Zn concentration in Sn has been observed at low Zn concentrations but a constant depth is approached for Zn concentrations greater than ∼0.08 atomic fraction.     

Effects of S,Si, or Fe dopants on the diffusion of Zn in InP during MOCVD

Diffusion of Zn in InP during growth of InP epitaxial layers has been investigated in layer structures consisting of Zn-InP epilayers grown on S-InP and Fe-InP substrates, and on undoped InP epilayers. The layers were grown by metalorganic chemical vapour deposition (MOCVD) atT = 625° C andP = 75 Torr. Dopant diffusion profiles were measured by secondary ion mass spectrometry (SIMS). At sufficiently high Zn doping levels ([Zn] ≥8 × 10¹⁷ cm⁻³) diffusion into S-InP substrates took place, with accumulation of Zn in the substrate at a concentration similar to [S]. Diffusion into undoped InP epilayers produced a diffusion tail at low [Zn] levels, probably associated with interstitial Zn diffusion. For diffusion into Fe-InP, this low level diffusion produced a region of constant Zn concentration at [Zn] ≈ 3 × 10¹⁶ cm⁻³, due to kick-out of the original Fe species from substitutional sites. We also investigated diffusion out of (Zn, Si) codoped InP epilayers grown on Fe-InP substates. The SIMS profiles were characterised by a sharp decrease in [Zn] at the epilayer-substrate interface; the magnitude of this decrease corresponded to that of the Si donor level in the epilayer. For [Si] ≫ [Zn] in the epilayer no Zn diffusion was observed; Hall measurements indicated that the donor and acceptor species in those samples were electrically active. All these results are consistent with the presence of donor-acceptor interactions in InP, resulting in the formation of ionised donor-acceptor pairs which are immobile, and do not contribute to the diffusion process.     

Planar Zn diffusion in InP

A procedure for achieving well-behaved planar Zn diffusion to a controllable depth in n-type InP is described. The dilute-Zn diffusion, which utilizes a Zn+Ga+P source (in an evacuated ampoule), is performed in the temperature range 650–700°C. The low diffusion temperatures employed assure that any previous junctions that might be prepared, such as LPE heterojunctions, are not affected by the diffusion process. The masking afforded by Si₃N₄ and partial “masking,” or attenuation, afforded by SiO₂ on InP are demonstrated. The results obtained suggest that dilute-Zn diffusion in InP, with a significant P over-pressure, favors a substitutional diffusion mechanism that probably follows a complementary error function distribution.     

Prevention of diffusion-induced defects in the fabrication of diffused electroluminescent GaP devices

Recent studies of Zn diffusion in GaP have prompted a re-evaluation of diffusion techniques for the fabrication of light-emitting GaP devices. Two diffusion sources differing essentially in the phosphorus partial pressure have been studied in a closed system. One is a ternary source consisting of Ga, P, and Zn. The other is a fully evaporating charge of ZnP₂. The Zn surface concentrations obtained by using the ZnP₂ source have been determined by surface barrier capacitance and by electron microprobe measurements. Diffusion-induced defects and nonplanar diffusion fronts have been studied by means of x-ray topography, the scanning electron microscope, and optical absorption. With appropriate choices of diffusion conditions and sources, it is possible to eliminate diffusion-induced lattice strain, minimize optical absorption, and also to obtain planar junctions. In suitably doped layers grown by the liquid phase epitaxy process (LPE), p-n junctions have been formed by Zn diffusion using a ZnP₂ source at 900°C. Two subsequent heat treatments were performed on red-emitting junctions, but no heat treatment was given to green-emitting junctions. The red test diodes yielded electroluminescent quantum efficiencies as high as 1.5% with typical values between 1.0 and 1.3% at a current density of 1 A/cm². Green emitting diodes with efficiencies of .05% at 100 ma (pulsed) have also been obtained.     

Pd/Zn/Pd/Au ohmic contacts to ρ-Type InP

Low resistance ohmic contacts (ρ_c = 7 x 10^-5 Ω-cm ² ) have been fabricated to Zn-doped p-type InP using an annealed Pd/Zn/Pd/Au metallization. Palladium reacts with InP at low temperatures to form a Pd₂InP ternary phase, which is initially amorphous but crystallizes and grows epitaxially on InP. Zinc reacts with some of the overlying Pd to form PdZn (≅250° C), which decomposes at 400-425° C to form PdP₂, freeing up Zn to diffuse into Au as well as InP. The contact resistance reaches a minimum as the decomposition reaction takes place. The resultant ohmic contact is laterally uniform and consists of epitaxial Pd₂InP adjacent to InP, followed by a thin layer of PdP₂ and then the outer Au layer. Further annealing leads to a breakdown of the contact structure,i.e. decomposition of Pd₂InP, and an increase in contact resistance.     

Pd/Sb(Zn) and Pd/Ge(Zn) ohmic contacts on p-type indium gallium arsenide: The employment of the solid phase regrowth principle to achieve optimum electrical and metallurgical properties

The development of two metallizations based on the solid-phase regrowth principle is presented, namely Pd/Sb(Zn) and Pd/Ge(Zn) on moderately doped In_0.53Ga_0.47As (p=4×10¹⁸ cm⁻³). Contact resistivities of 2–3×10⁻⁷ and 6–7×10⁻⁷ Ωcm², respectively, have been achieved, where both systems exhibit an effective contact reaction depth of zero and a Zn diffusion depth below 50 nm. Exhibiting resistivities equivalent to the lowest values of Au-based systems in this doping range, especially Pd/Sb(Zn) contacts are superior to them concerning metallurgical stability and contact penetration. Both metallizations have been successfully applied for contacting the base layer of InP/In_0.53Ga_0.47As heterojunction bipolar transistors.     

Zinc-doping of InP during chemical beam epitaxy using diethylzinc

Diethylzinc was used as ap-type dopant source during InP growth by chemical beam epitaxy. In InP, electrically activated Zn saturated at a concentration of ∼2.0 × 10¹⁸ cm⁻³ for epilayers grown at 540‡ C. Higher role concentrations were obtained by lowering the growth temperature. However, measurements with SIMS indicated that very serious Zn diffusion occurred when the Zn concentration appeared to reduce the pyrolysis efficiency of trimethylindium. This caused a reduction in the InP growth rate and InAs mole fraction in InGaAs epilayers. No Zn “memory effect≓ was detected in our system. Undoped InP epilayers maintained an n-type background of ∼5 × 10¹⁵ cm⁻³.     

Open-tube diffusion techniques for InP/LnGaAs heterojunctior bipolar transistors

Open-tube diffusion techniques used between 450 and 600° C are described which involve the supply of diffusant from a vapour source (via a solution) and a solid evaporated metal source. Investigations of Zn into InP and InGaAs(P) have been undertaken using both sources. SIMS profile analyses show that in the case of the vapour source the profiles indicate a concentration-dependent diffusion coefficient while the solid source diffusions can be well described by a Gaussian-type profile. The usefulness of the vapour source method has been demonstrated in the fabrication of bipolar transistors which exhibit good d.c. characteristics. The solid source method is limited by the slow diffusion velocity and more gradual profile. The InGaAs(P)/InP materials system has important applications in optical communications and future high speed microwave and switching devices. Useful technologies allied to the introduction of impurities into Si by diffusion, have gradually been emerging for use in the III-V semiconductor family. Closed tube systems1 have been used in order to contain the volatile group V species and prevent surface erosion. In addition, simpler open tube systems^2,3 have been developed that maintain a sufficient overpressure of the group V element. Zn and Cd p-dopants have been studied extensively because of the volatility and relatively large diffusion rates in III-V semiconductors. Opentube diffusion into both InP and InGaAs^2-6 has been studied but little detail has appeared concerning InGaAs and InGaAsP. In this paper we describe a comprehensive study of the diffusion of Zn into InP and InGaAs(P) using both open-tube vapour source and a Au/Zn/Au evaporated solid source with SiN_x acting both as a mask and also an encapsulant to prevent loss of Zn and decomposition of the substrate material. The techniques have been successfully applied to the fabrication of InP/lnGaAs heterojunction bipolar transistors which show good dc characteristics. Reference to InGaAs in the text implies the InP lattice-matched composition In_0.53Ga_0.47As.     

Capacitance-Voltage characteristics of metal-insulator-semiconductor diodes with S passivation and Si interface control layers on GaAs and InP

GaAs and InP surfaces have been prepared by gas-phase and liquid-phase polysulfide passivation techniques followed by the deposition of Si interface control layers (ICLs) by e-beam evaporation. For GaAs surfaces, the performance of an ICL consisting of 1.5 nm Si on top of 0.5 nm of Ge has also been evaluated. Metal-insulator-semiconductor diodes with aluminum top electrodes were fabricated on these surfaces using silicon nitride deposited by a remote plasma-enhanced chemical vapor technique or silicon dioxide deposited by a conventional direct plasma-enhanced chemical vapor deposition technique. The quality of the interfaces was analyzed by capacitance-voltage (C-V) measurements and the interface state densities D_it were deduced from the C-V data using the high-low method. Values as low as 1.5 × 10¹² eV⁻¹cm⁻² were obtained for polysulfide-passivated GaAs surfaces with a Ge-Si or Si ICL, the lowest ever demonstrated using the high-low method for an ex-situ technique not involving GaAs epitaxy. For InP, the Si ICL does not reduce D_it below that of 2 × 10¹² eV⁻¹ cm ⁻² that was obtained for the polysulfide passivated surface. The Si ICL produces an interface that degrades more slowly on exposure to air for both GaAs and InP.     

Dopant diffusion and current-voltage studies on epitaxial InP codoped with Ru and Fe

Semi-insulating Fe and Ru codoped InP epitaxial layers grown by low-pressure hydride vapor phase epitaxy have been investigated. InP∶Ru and InP∶Fe, Ru layers were grown on p-InP∶Zn andn-InP∶S, substrates, in order to study dopant diffusion and electrical characteristics. Dopant diffusion profiles of Ru, Fe and Zn were measured by secondary ion mass spectroscopy. A small but noteworthy diffusion front is observed when InP∶Ru is adjacent to InP∶Zn, but not when adjacent to n-InP. For InP∶Fe codoped with Ru a pronounced interdiffusion of Fe and Zn is observed for Ru concentrations less than 2 10¹⁷ cm⁻³, but for a higher Ru concentration the interdiffusion is clearly suppressed. Moreover, when InP is codoped with Fe and Ru, the small diffusion tail of Ru in InP∶Zn vanishes. Unlike InP∶Fe, resistivities above 1 10⁸ cm are measured for both electron and hole-current injection in InP∶Fe,Ru.     

Zn在Ge中扩散的研究

用Zn作扩散源在封闭的真空石英管中,研究了Zn在Ge中的扩散问题,给出了xj-t1/2关系和C-1/T关系,比较了扩散源温度对样品表面形貌的影响。采用双温区扩散工艺可获得表面光亮的样品。采用真空退火工艺可使扩散样品表面漏电流降低。     

Zn doping of InP, InAsP/InP, and InAsP/InGaAs heterostructures through metalorganic vapor phase diffusion (MOVPD)

Zinc incorporation by post-growth metalorganic vapor phase diffusion (MOVPD) is used to achieve high p-doping, which is desirable for the fabrication of photodiodes. Diethylzinc (DEZ) is used as precursor and Zn is diffused into InP and InAs_0.6P epitaxial layers grown by low pressure metalorganic vapor phase epitaxy (MOVPE) on different substrate orientations, enabling the investigation of the dislocation density on the Zn incorporation. Diffusion depths are measured using cleave-and-stain techniques, resistivity measurements, electrochemical profiling, and secondary ion mass spectroscopy. High hole concentrations of, respectively, 1.7 10¹⁹ and 6 10¹⁸ cm⁻³, are obtained for, respectively, InAs_0.60P and InP. The diffusion coefficients are derived and the Zn diffusion is used for the fabrication of lattice-mismatched planar PIN InAsP/InGaAs photodiodes.     

The luminescent properties of nitrogen doped GaAsP light emitting diodes

The properties of GaAsP:N light emitting diodes, which emit throughout the range from 7000 Å to 5500Å (red to green), have been investigated. The diodes were fabricated by Zn diffusion into n-type vapor phase epitaxial layers doped with nitrogen and tellurium. The emission spectra, luminous efficiency, quantum efficiency, brightness, and decay time constant have been investigated as functions of alloy composition. Also, the luminous output of the devices has been studied as a function of drive current density and temperature. In the yellow and green spectral regions the performance of nitrogen doped diodes is more than an order of magnitude better than that of nitrogen free diodes of equivalent peak emission wavelength. The luminous efficiency of diodes in the redamber spectral region, with alloy compositions near GaAs_0.35P_0.65 is equivalent to that obtained in GaP:Zn, O red emitting diodes with 2% quantum efficiency.     

Low-temperature Zn- and Cd-diffusion profiles in InP and formation of guard ring in InP avalanche photodiodes

Zn and Cd diffusion in InP were studied in the wide temperature range of 350-580°C to realize a guard ring in InP avalanche photodiodes (APD's). Hole-concentration profiles for Zn and Cd diffusions at various temperatures were found to be expressed by a unified empirical curve, which decreases exponentially with the distance from the surface, and abruptly decreases at the diffusion front. A graded junction can be formed by diffusion at temperatures lower than 500°C for the n-InP background carrier concentration of 1016cm-3, while an abrupt junction can be formed by higher temperature diffusion. Breakdown voltages for the graded-junction diodes formed by low-temperature diffusion were confirmed to be higher than those for the abrupt-junction diodes formed by the higher temperature diffusion. A guard ring formed by the low-temperature Cd diffusion enabled planar-type InP and InGaAs/InP APD's to have uniform multiplication in the photosensitive area without any edge breakdown.     

The lattice position of diffused Zn in InP

We have measured the substitutional fraction (f_s) for Zn atoms diffused into InP crystals using the proton-induced x-ray excitation (PIXE) technique. Diffusion times ranged from 15–60 min at 425–650° C. For several samples with diffusion depths in the range 0.75-3.7 μm (as determined by SIMS analysis), we find that the Zn impurity atoms reside almost totally on lattice sites: f_s = 0.9 ± 0.1. Contrary to results of an earlier study, we find no evidence for precipitates in the diffused layers. However, only ∼10^-3-10^-1 of the Zn is electrically active, consistent with Tuck and Hooper’s suggestion of neutral V_p Zn_In V_p complexes.     

Low pressure metalorganic chemical vapor deposition of InP and related compounds

The low pressure metalorganic chemical vapor deposition epitaxial growth and characterization of InP, Ga_0.47In_0.53 As and Ga_xIn_1-xAs_yP_1-y, lattice-matched to InP substrate are described. The layers were found to have the same etch pit density (EPD) as the substrate. The best mobility obtained for InP was 5300 cm² V⁻¹S⁻¹ at 300 K and 58 900 cm² V⁻¹ S⁻¹ at 77₂K, and for GaInAs was 11900 cm² V⁻¹ S⁻¹ at 300 K, 54 600 cm² V⁻¹ S⁻¹ at 77 K and 90 000 cm V⁻¹S⁻¹ at 2°K. We report the first successful growth of a GaInAs-InP superlattice and the enhanced mobility of a two dimensional electron gas at a GaInAs -InP heterojunction grown by LP-MO CVD. LP MO CVD material has been used for GaInAsPInP, DH lasers emitting at 1.3 um and 1.5 um. These devices exhibit a low threshold current, a slightly higher than liquid phase epitaxy devices and a high differential quantum efficiency of 60%. Fundamental transverse mode oscillation has been achieved up to a power outpout of 10 mW. Threshold currents as low as 200 mA dc have been measured for devices with a stripe width of 9 um and a cavity length of 300 um for emission at 1.5 um. Values of T in the range 64–80 C have been obtained. Preliminary life testing has been carried out at room temperature on a few laser diodes (λ = 1.5μm). Operation at constant current for severalthousand hours has been achieved with no change in the threshold current.     

Au/Ge/Ni ohmic contacts to n-Type InP

The relationship between the electrical properties and microstructure for annealed Au/Ge/Ni contacts to n-type InP, with an initial doping level of 10¹⁷ cm^-3, have been studied. Metal layers were deposited by electron beam evaporation in the following sequence: 25 nm Ni, 50 nm Ge, and 40 nm Au. Annealing was done in a nitrogen atmosphere at 250-400‡C. The onset of ohmic behavior at 325‡C corresponded to the decomposition of a ternary Ni-In-P phase at the InP surface and the subsequent formation of Ni₂P plus Au₁₀In₃, producing a lower barrier height at the InP interface. This reaction was driven by the inward diffusion of Au and outward diffusion of In. Further annealing, up to 400‡C, resulted in a decrease in contact resistance, which corresponded to the formation of NiP and Au₉ln₄ from Ni₂P and Au₁₀In₃,respectively, with some Ge doping of InP also likely. A minimum contact resistance of 10^-7 Ω-cm² was achieved with a 10 s anneal at 400‡C.