Reduced lateral diffusion and reverse leakage in Be-implanted GaAs1−xPxdiodes

Lateral Zn diffusion under the Si₃N₄ mask encountered in standard red GaAs_0.6P_0.4 light emitting diodes can be eliminated in Be-implanted junctions. Typical reverse leakage current for implanted devices is ～ 5nA compared with ～ 250nA for Zn-diffused diodes.     

Beryllium and sulfur ion-implanted profiles in gaas

Atomic profiles of ion-implanted Be and S in GaAs have been measured as a function of implant fluence and annealing temperature. Concentration versus depth profiles were ob-tained by means of secondary ion mass spectrometry (SIMS) techniques. Pyrolytically deposited and sputter-coated Si0₂ and Si₃N₄ films were used as encapsulants for the 500 to 900° annealing study. Semi-insulating GaAs was implanted with 200 keV³⁴S⁺ to fluences of 1 × 10¹⁴ and 5₂× 10¹⁴/cm², and 100 keV⁹Be⁺ in the 1 × 10¹³ to 1 × 10¹⁵/cm² fluence range. The S profiles did not change significantly after annealing at 800°C, although there was some skewing after annealing above 600°C. In contrast, the Be profiles showed significant changes and a decrease in the peak concentration for the ≥ 5 × 10^T4/cm² implants after a 700°C anneal. After a 800°C anneal the Be profile was essentially flat with a monotonic decrease from the surface into the implanted re-gion and a 900°C anneal caused a further decrease in the Be concentration. Profiles of Be implants of ≤ 1 × 10¹⁴/cm² did not change significantly after annealing indicating that the higher fluence cases were related to solubility effects. This work supported by the Naval Electronic Systems Command and the Office of Naval Research.     

Electrical properties of be-implanted GaA1-xPx

Hall effect and resistivity measurements on Be implanted GaAs_1-xP_x(x～0.38) indicate that essentially 100% doping efficiency may be obtained for normal Be concentrations after a 900°C anneal using either SiO₂ or Si₃N₄ as an encapsulant. The temperature dependence of hole mobility in these samples exhibits impurity banding effects similar to those reported in heavily Zn doped GaAs. Hall effect measurements in conjunction with successive thin layer removal techniques indicate there is no significant diffusion of the implanted Be during anneal for a fluence of 6×10¹³ ions/cm².     

Electrical properties and photoluminescence studies of Ge-implanted GaAs

Thedata presented here show that Ge- implanted GaAs has a complex amphoteric behavior which is controlled by the implantation dose, implantation temperature, and anneal temperature. Annealing was performed with rf plasma deposited Si₃N₄ as the encapsulant. Implantations at-100° C resulted in p-layers, while those performed at 100° C and above resulted in n-layers regardless of the dose and anneal temperature. Room temperature implants resulted in p- or n-layers depending on the combination of dose and anneal temperature. Electrical activation and carrier mobilities were low for anneal temperatures ≤ 850°C. Low temperature (6 K) photoluminescence indicated that a significant amount of residual damage remained after annealing. Atomic Ge distribution profiles, carrier con-centration profiles, and junction characteristics of Ge-implanted GaAs planar diodes are also presented. This work was supported by the Joint Services Electronics Program (U.S. Army, U.S. Navy, U.S. Air Force) under contract N00014-79-C-0424, and by the Office of Naval Research under contract N00014-76-C-0806.     

Photoreflection studies of band offsets at the heterojunction in strained short-period GaAs/GaAsP superlattices

Energies of band-to-band transitions with the involvement of the quantum-confinement subbands are determined from the photoreflection spectra of the strained short-period GaAs/GaAs_0.6P_0.4 superlattice. Strains caused by the mismatch of the crystal lattice in the GaAs and GaAs_0.6P_0.4 layers are calculated on the basis of the observed shift of the fundamental-transition energy in GaAs_0.6P_0.4. Positions of minibands in the superlattice are simulated in relation to the potential jump at the heteroboundary; the Kronig-Penney model is used in the calculations. Comparison of the results of simulation with experimental data shows that the studied superlattice is of type I with weakly localized electrons and light holes. The potential jump at the heteroboundary in the conduction band amounts to ΔE _c /ΔE _g =0.15.     

Phosphorus incorporation in GaAsP grown by remote-plasma MOCVD

Epitaxial layers of GaAs and GaAs_xP_1−x were deposited under a variety of conditions using a remote plasma in a metal-organic chemical vapor deposition (MOCVD) reactor. The remote rf plasma dissociated AsH₃ and PH₃ into highly reactive radicals increasing the growth rate at low temperatures and increasing the phosphorus incorporation at temperatures below 850° C. GaAs_xP_1−x with a high P content could be grown at low deposition temperatures by using the plasma to increase the reactivity of PH₃. The growth rate of both GaAs and GaAs_xP_1−x was increased at low temperatures and GaAs_xP_1−x was grown at temperatures down to 550° C.     

The effect of annealing temperature on the carrier concentration OF Hg0.6Cd0.4Te

The carrier concentration dependence of Hg_0.6Cd_0.4Te on annealing temperature for the Hg and Te saturation condi-tions is presented in this paper. At low annealing tempera-tures, T_A < 350‡ C, residual donor impurities apparently limit the carrier concentration. In contrast, at higher annealing temperatures, 350‡ C < T < 700‡ C, the stoichio-metric acceptor density is increased such that the residual donors are compensated and the material is converted to p-type with an acceptor density as large as 10¹⁷ cm⁻³ . An empirical expression describing this dependence of the acceptors on annealing temperature is given for both the Hg and Te saturation condition: P (Hg saturation) = 1.46 × 10²² exp (−0.84/kT_A), P (Te saturation) = 1.90 × 10¹⁸ exp (−0.15/kT_A). Supported in part by Air Force Materials Laboratory, WPAFB, Ohio under Contract AF61533-C-74-5041.     

Miscibility gap in the GaAsy Sb1−y system

Measurements have been made to determine accurately the solidus curve of the pseudobinary section GaAs_ySb_1−y, by annealing samples to equilibrium and determining compositions by x-ray powder photography. It is found that the equilibriui diagram shows a peritectic form with a peritectic temperature of 745 ± 1‡C and a miscibility gap at that temperature extending from y = 0.38 to y = 0.68. It is also shown that as the temperature is lowered the miscibility gap widens rapidly, being from y = 0.30 to y = 0.95 at 700‡C. The form of these phase boundaries is important when growth of GaAs_ySb_1−y alloys by liquid phase epitaxy or similar techniques is considered.     

Rapid capless annealing of28Si,64Zn,and9Be implants in GaAs

We report the use of tungsten-halogen lamps for rapid (−10 s) thermal annealing of ion-implanted (100) GaAs under AsH₃/Ar and N₂ atmospheres. Annealing under flowing AsH₃/Ar was carried out without wafer encapsulation. Rapid capless annealing activated implants in GaAs with good mobility and surface morphology. Typical mobilities were 3700–4500 cm²/V-s for n-layers with about 2×10¹⁷cm⁻³ carrier concentration and 50–150 cm²/v-s for 0.1–5xl0¹⁹ cm⁻³ doped p-layers. Rapid thermal annealing was performed in a vertical quartz tube where different gases (N₂, AsH₃/H₂, AsH₃/Ar) can be introduced. Samples were encapsulated with SiO when N₂ was used. Tungsten-halogen lamps of 600 or 1000 W were utilized for annealing GaAs wafers ranging from 1 to 10 cm² in area and 0.025 to 0.040 cm in thickness. The transient temperature at the wafer position was monitored using a fine thermocouple. We carried out experiments for energies of 30 to 200 keV, doses of 2×10¹² to 1×10¹⁵ cm⁻², and peak temperatures ranging from 600 to 1000‡C. Most results quoted are in the 700 to 870‡C temperature range. Data on implant conditions, optimum anneal conditions, electrical characteristics, carrier concentration profiles, and atomic profiles of the implanted layers are described. Presented at the 25th Electronic Materials Conference, Burlington, VT, June 22, 1983.     

Gallium distribution and electrical activation in Ga+-implanted Si

Gallium distribution profiles in Ga⁺-implanted silicon have been measured by secondary ion mass spectrometry (SIMS) and differential Hall effect methods. The previously reported penetrating tails are not observed for as-implanted samples. The redistribution of Ga during annealing is affected by ion damage and effects due to recrystallization of the amorphous layer. Electrical carrier profiles indicate that carrier concentration higher than the usual Ga solid solubility can be achieved in Ga-implanted Si recrystallized at 600‡C. However, this large acceptor concentration diminishes after higher temperature annealing. For 900‡C anneals, the carrier concentration is limited by the Ga solid solubility and some compensation due to unannealed ion damage. Work Supported by the Joint Service Electronics Program (U.S. Army, U.S. Navy, U.S. Air Force) under Contracts DAAB-07-72-C-0259 and DAAG-16-78-C-0016, and by the National Science Foundation under Grants DMR-77-22228, DMR-76-01058, and CHE-76-03694.     

Redistribution of implanted dopants in GaN

Donor (S, Se, and Te) and acceptor (Mg, Be, and C) dopants have been implanted into GaN at doses of 3–5×10¹⁴ cm⁻² and annealed at tem peratures up to 1450°C. No redistribution of any of the elements is detectable by secondary ion mass spectrometry, except for Be, which displays behavior consistent with damageassisted diffusion at 900°C. At higher temperatures, there is no further movement of the Be, for peak annealing temperature durations of 10 s. Effective diffusivities are ≤2×10⁻¹³ cm²·s⁻¹ at 1450°C for each of the dopants in GaN.     

P-type doping of GaAs by carbon implantation

The electrical properties of C-implanted <100> GaAs have been studied following rapid thermal annealing at temperatures in the range from 750 to 950°C. This includes dopant profiling using differential Hall measurements. The maximum p-type activation efficiency was found to be a function of C-dose and annealing temperature, with the optimum annealing temperature varying from 900°C for C doses of 5 × 10¹³ cm⁻² to 800°C for doses ≥5 × 10¹⁴cm⁻². For low dose implants, the net p-type activation efficiency was as high as 75%; while for the highest dose implants, it dropped to as low as 0.5%. Moreover, for these high-dose samples, 5 × 10¹⁵ cm⁻², the activation efficiency was found to decrease with increasing annealing temperature, for temperatures above ∼800°C, and the net hole concentration fell below that of samples implanted to lower doses. This issue is discussed in terms of the amphoteric doping behavior of C in GaAs. Hole mobilities showed little dependence on annealing temperature but decreased with increasing implant dose, ranging from ∼100 cm²/V·s for low dose implants, to ∼65 cm²/V·s for high dose samples. These mobility values are the same or higher than those for Be-, Zn-, or Cd-implanted GaAs.     

Hydrogen concentration profiles and chemical bonding in silicon nitride

The complementary techniques of nuclear reaction analysis and infrared absorption were used to study the concentration profiles and chemical bonding of hydrogen in silicon nitride for different preparation and annealing conditions. Silicon nitride prepared by chemical vapor deposition from ammonia-silane mixtures is shown to have hydrogen concentrations of 8.1 and 6.5 at.% for deposition temperatures of 750 and 900‡C, respectively. Plasma deposition at 300‡C from these gases result in hydrogen concentrations of ~22 at.%. Comparison of nuclear reaction analysis and infrared absorption measurements after isothermal annealing shows that all of the hydrogen retained in the films remains bonded to either silicon or nitrogen and that hydrogen release from the material on annealing is governed by various trap energies involving at least one Si-H and two N-H traps. Reasonable estimates of the hydrogen release rates can be made from the effective diffusion coefficient obtained from measurements of the spreading of the implanted hydrogen distribution upon annealing. This article sponsored by the U. S. Department of Energy under Contract AT(29-1)-789.     

Phosphorus diffusion in gallium arsenide

The formation of monocrystalline GaAs_1?xP_x by the solid state diffusion of phosphorus into monocrystalline GaAs at a phosphorus pressure of 35 atm has been confirmed by X-rays and reflectivity measurements. Phosphorus distribution in GaAs specimens diffused in the temperature range 800–1100°C has been determined by reflectance studies. The diffusion coefficient and the activation energy computed from the known phosphorus distributions in the diffused specimens are found to depend on the content of phosphorus in the diffused region. The variation of the depth of GaAs_1?xP_x-GaAs junction with time (at a fixed temperature, 1000°C) and temperature (for a fixed time, 24.5 hr) has been studied.     

Pulsed laser annealing of self-organized InAs/GaAs quantum dots

The effect of pulsed laser annealing (PLA), using an excimer laser, on the luminescence efficiency of self-organized InAs/GaAs and In_0.4Ga_0.6As/GaAs quantum dots has been investigated. It is found that such annealing can enhance both the peak and integrated photoluminescence (PL) efficiency of the dots, up to a factor of 5–10 compared to as-grown samples, without any spectral shift of the luminescence spectrum. The improved luminescence is attributed to the annealing of nonradiative point and extended defects in and around the dots.     

Effects of contact metals on minority carrier diffusion lengths in GaAs

Contact technology for GaAs involves optimizing such factors as contact resistance or Schottky barrier height, alloy cycle conditions, thermal ageing, adhesion, and ease of high resolution processing. Minority carrier properties may be significantly degraded by in-diffusing contact metals. At typical alloying conditions of 10 sec at 500° C, Ni diffuses at least 10 μm and reduces the hole diffusion length (L_p) in vapor phase epitaxial GaAs from 4.4 to 1.7 ym. At 600°C, L_p becomes 1.0 μm. Other metals, such as Fe, Pt, and Cr, significantly improve L_p in VPE GaAs. L_p increases from 3.0 to 5.0 μm for an Fe diffusion of 5 minutes at 500°C. These improvements may be due to interaction of in-diffused Fe with recombination centers, such as Ga vacancy complexes or Ni. Fe causes increases in minority carrier diffusion lengths also in n and p type ingot GaAs, though 800 – 900°C diffusions are required and at these temperatures the doping is significantly changed by Fe acceptors.     

Specific contact resistivity of indium contacts to n-type CdTe

Indium alloyed to n-type CdTe of about 10¹⁶ cm^-3 electron concentration provides a contact resistivity of about 7 x 10^-3 ohm cm². This is achieved by alloying for 10 minutes at 150-450‡C in a sealed ampoule with an overpressure of cadmium. If the alloying is done in an open tube H₂ flow without a Cd vapor overpressure, alloying temperatures above 250‡C cause the contact resistance to rise as cadmium vacancies increase the compensation in the CdTe. Further improvement of the contact resistivity to 1 x 10^-3 ohm cm is obtained by a 900‡C diffusion of In into the n-CdTe (electron concentration 10¹⁶ cm^-3 before the diffusion).     

Novel Cu/Cr/Ge/Pd Ohmic Contacts on Highly Doped n-GaAs

The thermal stability of the Cu/Cr/Ge/Pd/n⁺-GaAs contact structure was evaluated. In this structure, a thin 40 nm layer of chromium was deposited as a diffusion barrier to block copper diffusion into GaAs. After thermal annealing at 350°C, the specific contact resistance of the copper-based ohmic contact Cu/Cr/Ge/Pd was measured to be (5.1 ± 0.6) × 10⁻⁷ Ω cm². Diffusion behaviors of these films at different annealing temperatures were characterized by metal sheet resistance, X-ray diffraction data, Auger electron spectroscopy, and transmission electron microscopy. The Cu/Cr/Ge/Pd contact structure was very stable after 350°C annealing. However, after 400°C annealing, the reaction of copper with the underlying layers started to occur and formed Cu₃Ga, Cu₃As, Cu₉Ga₄, and Ge₃Cu phases due to interfacial instability and copper diffusion.     

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.     

Characterization of GaAs substrates and epitaxial GaAs1−xPx layers by divergent x-ray beam diffraction

The application of the divergent x-ray beam diffraction method was studied for characterizing lattice imperfections, lattice parameters and composition variations and lattice strain in GaAs substrates and in GaAs_1−xP_x epitaxial layers. Reflection conics from {117}, {026}, {155} and (004) planes predominate in pseudo-Kossel back reflection patterns obtained from samples with (001) orientations. The sensitivity of pseudo-Kossel line displacements is assessed for lattice parameter and anisotropic strain distortion measurements. The lattice parameter of GaAs was determined to be 5.6435 ∢. Moseic subgrain misorientations in GaAs_1−xP_x epitaxial layers were found to be relatively independent of graded layer composition gradients, whereas homogeneous stress distortion was more strongly dependent.