High-purity semi-insulating GaAs material for monolithic microwave integrated circuits

Liquid-Encapsulated Czochralski (LEC) growth of large-diameter bulk GaAs crystals from pyrolytic boron nitride (PBN) crucibles has been shown to yield high crystal purity, stable high resistivities, and predictable direct ion-implantation characteristics. Undoped (≲low 10¹⁴cm^-3chromium) and lightly Cr-doped (low 10¹⁵cm^-3range) -GaAs crystals, synthesized and pulled from PBN crucibles contain residual shallow donor impurities typically in the mid 10¹⁴cm^-3, exhibit bulk resistivities above 10⁷Ω . cm, and maintain the high sheet resistances required for IC fabrication (>10⁶Ω/□) after implantation anneal. Direct²⁹Si channel implants exhibit uniform (± 5 percent) and predictable LSS profiles, high donor activation (75 percent), and 4800- to 5000-cm²/V . s mobility at the (1 to 1.5) × 10¹⁷cm^-3peak doping utilized for power FET's. It has also been established that LEC crystals can provide the large-area, round     

Undoped semi-insulating LEC GaAs: a model and a mechanism

Undoped semi-insulating GaAs grown by the high-pressure liquid encapsulated Czochralski (LEC) method has been produced for use in direct ion implantation in several laboratories.1?4 A clear understanding of the factors controlling impurity transport and compensation in these materials has been lacking to date. In this work, detailed characterisation has been performed on undoped semi-insulating crystals grown from both SiO2 and PBN crucibles followed by a proposed impurity model and compensation mechanism.     

Quartz versus PBN—The effect of crucible type on undoped LEC GaAS

Undoped semi-insulating GaAs crystals were grown in a low pressure LEC system using quartz and pyrolytic boron nitride (PBN) crucibles. Crystals grown in PBN crucibles are consistently semi-insulating from the seed end to the tail end. Crystals grown in quartz crucibles have lower Hall mobility. Other properties such as dislocation etch-pit of conductive material beginning from the seed end of the crystal, and have lower Hall mobility. Other properties such as dislocation etch-put density, implant profile, and thermal conversion characteristics of the two types of crystal are about the same.     

改进的低压LEC法生长半绝缘GaAs单晶

本文提出了改进的低压LEC/PBN法获得稳定的熔体化学计量比的条件,研究了晶体的电学性质、位错密度、C含量及EL2浓度等特性,并考察了高温热处理对晶体特性的影响.     

Temperature dependence of FET properties for Cr-doped and LEC semi-insulating GaAs substrates

The temperature dependence of carrier concentration and mobility profiles is measured on Schottky-barrier gate FET's formed by Si implantation into intentionally Cr-doped Czochralski-grown semi-insulating GaAs substrates and LEC semi-insulating GaAs substrates. The effective depth of the channel implant is at least 100 nm shallower for Cr-doped substrates than it is for LEC substrates. Carrier mobilities are higher for LEC substrates; at low temperature, mobility is higher at the channel-substrate interface than it is nearer the surface. Devices on both types of substrates show free-carrier trapping effects between 160 and 225 K. For LEC substrates, traps are on the channel side of the active channel-substrate interface. For Cr-doped substrates, observation of traps depends on biasing the FET beyond pinchoff; traps are on the substrate side of the channel-substrate interface.     

Characterization of horizontal Bridgman-grown semi-insulating GaAs for ion implantation

Thermal stability of horizontal Bridgman-grown (HB) Cr-doped seme-insulating GaAs is characterized systematically by leakage current measurement. Electrical characteristics for a Si-ion implanted n-layers on GaAs were evaluated by Hall and C-V measurements. The threshold voltage uniformity for MESFETs fabricated on implanted n-layer was also discussed. Not only the leakage current of annealed wafers but also the electrical properties of the ion implanted n-layers have a close correlation with the Cr concentration in the bulk GaAs. The uniformity of the ion implanted n-layer was degraded by the Cr concentration variations in the wafer. In addition to uniformity, mobility data, which show lower values for HB crystals than for undoped LEC crystal, imply the importance of high purity GaAs semi-insulating LEC crystal.     

Edge-photoluminescence concentration dependence in semi-insulating undoped GaAs

Dependences of the spectral peak position of edge photoluminescence, its half-width, resistivity, charge carrier mobility in crystals of semi-insulating undoped GaAs on the carbon concentration N _C at 77 K (3.0×10¹⁵ cm^?3≤N _C≤4.3×10¹⁶ cm^?3) were studied. The dependences observed are explained by the interaction of charge carriers with ionized impurity atoms and with structural defects.     

Growth of low dislocation density InP single crystals by the phosphorus vapor controlled LEC method

Low dislocation density <100> InP single crystals have been grown by a phosphorus vapor controlled LEC method (PC-LEC). 3 inch S-doped and Fe-doped InP and 2 inch Sn-doped InP single crystals have been grown by this method. In S-doped crystals, the dislocation free area could be increased compared with that of conventional LEC crystals. 3 inch Fe-doped InP with the dislocation density lower than 10⁴ cm^?2 could also be grown. The average EPD was lower than 5×10³ cm^?2 in 2 inch Sn-doped InP. The photoluminescence intensity of PC-LEC crystals was much higher than that of conventional LEC crystals in the case of Sn-doped InP.     

EPD measurements for low dislocation density GaAs and InP substrates

The Japan Manufacturers' Society of Compound Semiconductor Materials (JAMS-CS) performed etch pit density (EPD) round robin evaluations of undoped semi-insulating GaAs substrates for three years from 1986 to 1988 [1]. More than ten years have passed since then, and with applications for semiconductor lasers escalating, the market for low dislocation density substrate is increasing rapidly. EPD measurements for low dislocation density substrates are obviously different from that of a conventional semi-insulating GaAs substrate with EPD around 1.0 × 10⁴ cm⁻².     

Non-destructive characterization of electrical uniformity in semi-insulating GaAs substrates by microwave photoconductance technique

A novel non-destructive way of characterizing electrical uniformity of semi-insulating GaAs substrates is presented, and applied to Cr-doped HB and undoped LEC wafers. The method utilizes photoconductance at microwave frequencies. Photoconduction is shown to be n-type in both type of substrates, and its magnitude is related to effective lifetime of photo-generated electrons on the basis of a simple theory developed here. Photoconductance variation in Cr-doped substrates is less pronounced, and is related to Cr acceptor concentration. On the other hand, photoconductance variation is more pronounced in undoped LEC substrates with U,M or W-shaped distribution. The photoconductance variation in LEC substrates reflects concentration fluctuation of residual acceptor such as carbon. The photoconductance technique collects information concerning the acceptor distribution near the surface which has a direct effect on the threshold voltage of FETs.     

InP-on-CdS thin film heterostructures

Thin films of InP were deposited on single crystals and thin films of CdS by the planar reactive deposition technique. Good local epitaxy was observed on single crystals of CdS as well as InP and GaAs. The electrical evaluation of unintentionally doped films on semi-insulating InP substrates show them to be n-type with room temperature electron concentrations ranging from 5 × 1016 cm⁻³ to 5 × 10¹⁷ cm⁻³ and mobilities up to 1350 cm²/Vsec. For films intentionally doped with Mn and Be, p-type films were obtained. For Mn doping (deep acceptor level), room temperature mobilities as high as 140 cm²/Vsec and free carrier concentrations as low as 5 × 10¹⁶ cm⁻³ (with dopant level of 3 × 10¹⁸ cm⁻³) were obtained. For Bedoped films, free carrier concentrations of about 5 × 10¹⁸ cm⁻³ and mobilities of 20 cm²/Vsec were found. Scanning electron microscope and microprobe pictures show appreciable interdiffusion between the InP/CdS thin-film pair for InP deposited at 450°C. The loss of Cd from the CdS and the presence of an indium-cadmium-sulfur phase at the InP/CdS interface were observed. Interdiffusion is alleviated for InP deposition at lower temperatures. Supported in part by ERDA and AFOSR.     

Characterization of electron traps in ion-implanted GaAs MESFET's on undoped and Cr-doped LEC semi-insulating substrates

This paper presents the results of characterization of deep levels in ion-implanted layers on semi-insulating LEC GaAs substrates, using MESFET channel current DLTS and transient resistance techniques. Test devices on undoped substrates show six electron traps with activation energies ranging from 0.15 to 0.85 eV, and devices on lightly and heavily Cr-doped substrates show five-and two-electron traps, respectively. The well-known EL2 level is the dominant level in undoped and lightly Cr-doped material, and there are two-electron traps (0.22 and 0.85 eV) that exist only in undoped material, and with the addition of Cr they are suppressed and a new level at 0.64 eV emerges instead. A deep level at 0.53 eV was observed in all samples and whether this arises due to implantation and annealing or it is a characteristic of the LEC material is as yet unknown.     

Liquid encapsulated czochralski pulling of InP crystals

The growth of bulk indium phosphide crystals via liquid encapsulated Czochralski pulling from both stoichiometric and nonstoichiometric melts is described. Nominally un-doped crystals with carrier concentration N_D-N_A = 6 × 10¹⁵ cm⁻³ and Hall mobilities of 4510 cm²/Vsec at room temperature were grown. Also, we prepared Zn-or Cd-doped p-type crystals in the range 10¹⁶ ≤ N_A-N_D ≤ 10¹⁸ cm⁻³ with Hall mobilities ≤ 130 cm²/Vsec and Sn-doped n-type crystals in the range 4 × 10¹⁷ ≤ N_A-N_D ≤ 10¹⁸ cm^-3 with Hall mobilities ≤ 2400 cm²/Vsec. The dislocation density of LEC pulled InP crystals is typically ~ 10⁴ cm⁻².     

High purity InxGa1−xSb single crystals with cutoff wavelength of 7–8 µm grown by melt epitaxy

For the first time, InGaSb single crystals with a cutoff wavelength of 7–8 μm were successfully grown on GaAs substrates by a new growth technique named melt epitaxy. The band gap of InGaSb layers obviously narrowed compared with those with the same compositions grown by ordinary methods and the longest cutoff wavelength reached 8.3 μm. High electron mobility of 8.05×10⁴ cm²/Vs and low carrier density of 1×10¹⁵ cm⁻³ at 77 K were obtained indicating high purity of InGaSb epilayers.     

Growth and led evaluation ofN-type conductive lec gaas co-doped with in and si

Dislocation-free and low dislocation densityn-type conductive GaAs crystals, 50 mm in diameter, were grown by the In and Si co-doping LEC technique. Two-dimensional LED arrays were fabricated on substrates obtained from these crystals by the MOCVD technique and the influence of the In doping on the LED characteristics was examined. The light output power of LEDs fabricated on co-doped substrate with an In concentration of 1 ×10²⁰atoms/cm³ are low and are non-uniformly distributed, as compared with the boat-grown substrate, even though the co-doped substrate is dislocation-free. However, the LED properties of a substrate with an In concentration of 2 × 10¹⁸atoms/cm³ are the same as those of a boat-grown substrate. The light output power of the LEDs becomes higher as the In concentration in the substrate decreased.     

High purity and chrome-doped GaAs buffer layers grown by liquid phase epitaxy for mesfet application

High purity GaAs buffer layers of carrier concentration in the low (l-5)×l0^l4/cm³ range with 77K electron mobility over 100,000 cm²/V-sec and 300K mobility around 8000 cm?/ V-sec have been grown by liquid phase epitaxy on Cr-doped GaAs substrates using the graphite sliding boat method. The high purity has been achieved with systematic and concurrent long term bake-outs (24 hrs) of both LPE melt and substrate, both exposed to the H₂ ambient gas stream at 775?C, prior to epitaxial growth at 700?C. Substrate surface degradation was reduced by using Ga:GaAs etch melts that were undersaturated at 700?C by 5? to 40?C. Best buffer layer morphologies with regard to surface planarity were obtained using etch melts that were saturated by near 85% of weight of GaAs at 700°C. The importance of substrate preconditioning in order to achieve the low ( 1 -2)×l0¹⁴ was examined and found to be critical. Melt and substrate bake outs at 800?C, and use of a 40?C undersaturated etch melt prior to epitaxial growth at 800?C resulted in a p-type layer of carrier concentration, 1 .9×l0^l2/cm³ and resistivity 1×10⁵ ohm-cm. Chromium doping at 700?C resulted in buffer layers with sheet resistivities greater than 10 ohms/sq and low pinhole densities.     

Dislocation-free undoped semi-insulating GaAs epilayers prepared by chloride chemical vapor deposition and successive wafer annealing

Dislocation-free (DF) undoped semi-insulating GaAs epilayers have been realized by chloride chemical vapor deposition and successive wafer annealing. It was found that undoped conductive DF GaAs epilayers grown on Si-doped n-type DF GaAs substrates can be converted to semi-insulating by wafer annealing at temperatures higher than 950°C. The resistivity of these semi-insulating epilayers was higher than 10⁷ Ωcm. The outdiffusion of Si from the substrate to the epilayer was analyzed by secondary ion mass spectrometry and it was found that the thickness of the outdiffusion region was only 1μm.     

Zn-Doped InGaP Grown by the LP- MOCVD

Zn-doped In_0.485Ga_0.515P epitaxial layers were grown on semi-insulating GaAs substrates by low pressure metalorganic chemical vapor deposition (LP-MOCVD) at the temperatures 520,560, and 720°C. Growth conditions were optimized with respect to surface morphology for each growth temperature and the growth rates were in the range from 0.6 to 1.4 μm/h. Diethylzinc was used as a Zn precursor and the dependencies of hole concentrations, mobilities, and photoluminescence spectra on the growth conditions were studied. Doping levels from 3 × 10¹⁷ to 3 × 10¹⁸ cm⁻³ were obtained at different growth temperatures. The highest hole mobilities were measured in the layers grown at 560°C. The acceptor activation energy of 21 meV was measured from the photoluminesce spectra in our samples. As the results are not directly comparable with the data from the literature, theoretical models of Zn incorporation are discussed. A desorption energy of 0.55 eV of Zn atoms was calculated from the temperature dependence of the zinc distribution coefficient K_zn .     

Growth and characterization of Si doped vapor phase epitaxial GaAs for mesfet

This paper describes the Si-doping of GaAs that was grown using the AsCl₃:H₂:GaAs, Ga Chemical vapor deposition process. The doping sources were AsCl₃:SiCl₄ liquid solutions which proved to be highly reproducible for Si doping within the range, 1×1O¹⁶ to 2×10¹⁹ cm^?3. Incorporation of Si into the GaAs apparently occurs under near equilibrium conditions. This point is considered in detail and the consequences experimentally utilized to grow n, n+ bilayers using a single AsCl₃:SiCl₄ doping solution. Si impurity profiles based upon differential capacitance and SIMS data are presented. These can be very abrupt for n, n⁺ structures with order of magnitude changes occurring within 500 Å. For the 1×10₁₆ to 8×l0¹⁸ cm^?3 doped samples the mobilities at 78 and 298°K are comparable to the higher values reported for GaAs thin films grown by CVD. Power FET devices made from this material have demonstrated an output density of 0.86 watts/mm at 10 GHz.     

A direct comparison of LEC GaAs grown using low- and high-pressure techniques

A direct comparison has been made between the properties and implant behavior of undoped semi-insulating (SI) low- and high-pressure liquid encapsulated Czochralski (LEC) GaAs. Although the properties of high-pressure LEC had previously been well characterized, this is the first detailed study of the quality of low-pressure LEC material. It is shown that both material types are similar in structural quality, purity, and in the characteristics of conducting layers formed by direct ion implantation. Arsenic-rich melts and B2O3with greater than 500-ppm H2O content are required for obtaining reproducible and stable SI behavior growing from quartz crucibles.