Nonstoichiometry and nonradiative recombination in GaP

models which have been successful in explaining observations of other defect phenomena are used to identify the native nonradiative recombination center in GaP. It is concluded to be the complex V_Ga ⁻ P_Ga ⁺²V_Ga ⁻ acting via the configuration coordinate mechanism. It is believed to form during the cooling of the crystals from the quasi-equilibrium distribution of defects present during growth. Recent direct lattice-imaging experiments in GaAs have observed the corresponding defect complex in a concentration close to that predicted. It is predicted that the defect in GaP will exhibit recombination-enhanced diffusion.     

Deep-level recombination spectroscopy in GaP light-emitting diodes

Deep-level parameters determined from an analysis of the differential coefficients of the forward-bias current-voltage curves are compared in the example of commercial GaP LEDs. It is shown that these parameters are suitable for deep-center diagnostics. The proposed measurements can be performed on semiconductor wafers in the industrial environment without sealing or dividing into individual crystals. Fiz. Tekh. Poluprovodn. 33, 723–726 (June 1999)     

A scanning electron microscope study of the cathodoluminescence in GaP led material

Cathodoluminescence in GaP doped with zinc and oxygen has been studied using a scanning electron microscope. In p-n structures grown by liquid epitaxy, a region of low luminescent efficiency is found near to the junction. This is explained by a higher concentration of non-radiative centres, due to either growth defects or impurities. Lamps made by double liquid epitaxy on pulled substrates increase in efficiency when annealed. No such increase occurs for layers grown by single or double liquid epitaxy on vapour grown substrates. The increase is correlated with the movement of the edge of the cathodoluminescent region towards the junction in the first case only.     

Electroluminescent recombination near the energy gap in GaP diodes

The forward bias electroluminescence mechanisms at low temperatures in as-grown GaP diodes can be identified by comparison with photoluminescence results. The spectra consist of bound exciton transitions, many sharp lines due to donor-acceptor pair recombination and broad-band donor-acceptor recombination. The bound exciton lines are split, perhaps by the junction field. By studying the spectra as a function of temperature, the room temperature green emission is probably to be identified as a transition involving a deep donor associated with a subsidiary conduction band minimum. In more heavily doped junctions the fine structure becomes less well defined, but the general assignments remain. Some of the properties of these emission peaks, including efficiencies and kinetics, are described.     

The dislocation origin and model of excess tunnel current in GaP p-n structures

An excess tunnel current in GaP epitaxial nondegenerate p-n junctions on GaP and Si substrates was studied. An important experimental result is that the slope of exponential current-voltage (I–V) characteristic (in lnI–V coordinates) is independent of the width of the space-charge region, i.e., on n-and p-region doping levels. This fact is unexplained by existing models. A dislocation shunt model based on multihop tunneling through a dislocation line, which may be considered as a chain of parabolic potential barriers, is proposed. The density of dislocations predicted by this model is in agreement with the transmission electron microscopy (TEM) observations.     

SEM and Positron Annihilation Technology Investigation on the Defect Change with Thermal Treatment Temperature in GaP

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Deep level spectroscopy,low temperature defect motion and nonradiative recombination in GaAs and GaP

Recent developments in junction capacitance measurements allow deep levels in semiconductors to be conveniently studied for the first time. Experiments carried out on deep levels in GaP and GaAs show that the levels are often strongly coupled to the lattice. This coupling can cause rapid nonradiative recombination in which the released electronic energy causes violent vibrations of the lattice near the defect. The vibrations can promote low temperature defect motion. These two phenomena, nonradiative recombination and defect motion, are fundamental to the understanding of how defects limit the efficiency of light emitting devices and cause junction devices to degrade when forward biased. The recent work of Lang on deep level spectroscopy, Lang and Kimerling on defect motion and Henry and Lang on nonradiative recombination by multiphonon emission will be reviewed.     

Nitrogen implantation into GaP: Damage and nitrogen location studies

Implantations of 80 and 40 keV nitrogen into GaP have been carried out. The implants were performed at temperatures from 25° to 400°C for total doses in the range 10¹⁵ to 10^l6 cm⁻². Backscattering and channeling techniques have been used to determine the associated damage and its annealing characteristics for temperatures up to 800°C . Also determined, has been the lattice location of the implanted nitrogen. This was performed by implanting with the isotope¹⁵N and using the¹⁵N (p,α_o)¹²C nuclear reaction in conjunction with channeling techniques using a l MeV proton beam. Results indicate that the GaP is totally damaged following 25°C implants with 10¹⁵N⁺cm⁻². After annealing to 800°C , 70% of the damage has recovered. For implants above 100°C the initial damage is ~15%. Lattice location studies on samples implanted above 150°C show that following an 8 × 10¹⁴N⁺cm⁻² implant, ~60% of the nitrogen is located substitutionally. The substitutional content is reduced to 33% for an 8 × 10^l5N⁺cm^-2 implant. For anneals above 600°C the nitrogen is found to move off the substitutional sites. The results show that using ion implantation at elevated temperatures it is possible to obtain high concentrations of substitutional nitrogen in relatively damage free space.     

Noise in cathodoluminescence light

A theory is given of the noise in cathodoluminescence light and the results are compared with experiments on Sylvania 5BNP16 and RCA5WP11 cathode-ray tubes. The measurements indicate that the noise in cathodoluminescence is mainly caused by the shot noise of the primary beam. The noise intensity is proportional to the magnitude of the voltage applied to the tube for voltages above 10 kV. The spectral distribution of the noise corresponds to the square of the frequency response of the cathode-ray tube screen as expected theoretically. The application to light amplifiers is discussed.     

Luminescence decay kinetics in GaP:Bi and GaP:N

The lifetime of excitons bound to isoelectronic traps in GaP is studied as a function of temperature, excitation energy and intensity. The photoluminescence was excited both selectively and above the gap by using a pulsed, tunable dye laser with photon flux varying in the range of 10¹⁴–10¹⁹ photons/cm² per pulse. GaP:Bi shows a strong intensity dependence of τ(T) in the temperature range of 40–60 K due to the thermal activation of the electron. Similarly, GaP:N shows this behavior in the range of 20–100 K. In this case, two activation processes can be identified: release of the bound exciton into the free exciton band and dissociation of the exciton. The observed dependence of τ(T) on both excitation energy and intensity indicate that saturable deep traps (shunt paths) deplete the excess free carriers. These traps can be completely saturated in GaP:N while only partial saturation is achieved in GaP:Bi. The kinetic equations are written for GaP:Bi and solved numerically assuming quasiequilibrium conditions. Fitting this model to the experimental results yields the capture cross sections for carriers by Bi and by the deep traps as well as the concentration of the latter.     

New microwave techniques in surface recombination and lifetime studies

A new method of measurement of recombination effects in semiconductors is described. Germanium and silicon slabs are prepared to fill the cross section of a waveguide and changes in microwave transmission as a function of conductivity of the semiconductor provide a direct measurement of lifetime. It is shown that under specific conditions of thickness of the sample a linear relationship exists between the transmitted power and the conductivity, even when the conductivity approaches the value of the product of angular frequency and permittivity. Furthermore, the new technique of lifetime measurement is simpler than previously described microwave and conventional dc methods and can be used to cover a broader range of conductivities. Experimental data are given to illustrate the principles.     

Electron-hole plasma luminescence in GaP

An experimental investigation of the luminescence of strongly excited “pure” GaP has been performed as function of input light intensity and temperature. Three distinct situations are observed. For T < 25K, the spectrum consists of a band, due to the recombination of the electron-hole liquid (EHL), coexisting with an exciton-rich gas phase. At T 40K, the EHL band is still apparent, but the gas has evolved into an electron-hole plasma (EHP). Finally, at T > 60K, only the EHP recombination remains and exhibits a density dependent lineshape as expected. The density at which the metal-insulator Mott transition occurs is compared to the calculations using the Debye-Hückel criterion.     

Two-carrier space-charge-limited current in GaP

Junctions have been made in GaP which become p⁺-i-n⁺ structures at low temperatures. At high forward bias, the current voltage characteristic may be ascribed to two-carrier space-charge-limited current. This interpretation permits estimates of the electron mobility, the electric field at which the electron drift velocity saturates, the recombination kinetics and trapping effects. The techniques necessary to provide good ohmic contact to both n- and p-type GaP are described. These contacts permit measurement of the diode characteristics at high current levels and low temperatures.     

卤水-氨法制备碱式氯化镁纤维的SEM研究

纤维状碱式氯化镁是制备优良纤维状阻燃剂氢氧化镁或氧化镁晶须的重要中间体，它的结晶质量，微观内应变的大小等因素，对后续产物具有决定性的作用。要制得结晶性能好、长径比大的纤维状氢氧化镁和MgO晶须，首枯条件是制得长径比大、结晶较完美的纤维状碱式氯化镁。我们利用扫描电镜（SEM）研究了制备条件对其微观形态的影响。     

Output saturation in GaP red lamps

The variation of light output with current in a diode lamp is analysed. It is assumed that, while luminescent recombination processes saturate at high current, competing nonluminescent processes do not. The derived relationship is compared with published experimental work.     

Properties of deep Cu levels in GaP

Optical properties of two Cu-induced deep acceptorlike levels in GaP with binding energies E_A = 0.50 ± 0.01 eV and E_B 0.7 eV have been investigated. Data are reported here from purely optical techniques, based on detection of photoluminescence. A detailed spectral analysis of the broad Cu-related 1.65 eV-emission reveals a moderate Frank-Condon shift Δ_FC 105 ± 15 meV for the A-center. Accurate spectral data for optical cross section σ_pA⁰(hν) and σ_nA⁰(hν) were measured for the 0.50 eV A-center. Optical cross sections σ_pB⁰(hν) and σ_nB⁰(hν) could also be measured via luminescence, in spite of the fact that the B-center appears to have a completely nonradiative recombination.     

Dislocation-limited minority-carrier lifetime in n-type GaP

Minority hole lifetimes as high as 2.5 ?s have been reproducibly obtained in epitaxial GaP layers grown by an isothermal liquid-phase technique. In this material, the measured lifetimes are shown to be controlled by the dislocation density ?D in the samples when ?D > 5 × 104 cm?2. A theory is presented which shows that, when the lifetime is dislocation limited, its value is close to a minimum possible value for recombination at the dislocation cores.     

High-temperature electron mobilities in LPE-Grown GaP

We report measurements to 500°C of resistivity and Hall mobility in Sn-doped, n-type GaP grown by liquid phase epitaxy. Samples with room-temperature carrier densities between 1 × 10¹⁶ and 1 × 10¹⁸cm⁻³ were studied. Mobilities were in the range 100–180 cm²/V-sec at room temperature and in the range 27–35 cm²/V-sec at 400°C. Carrier densities increased by only about a factor of two with increasing temperature. Theoretical fits to the mobility data were made by considering contributions from intervalley, polar-optic, acoustic-deformation-potential, and ionlzed-impurity scattering mechanisms. Our results confirm the utility of GaP for high-temperature device applications and provide important information on electrical parameters needed for device modeling and design.     

p-n-junction photovoltaic effect in zinc-doped GaP

The p-n-junction photovoltaic effect in Zn-doped GaP was studied as a function of various parameters. The spectral sensitivity, the temperature dependence of the short-circuit current and the open-circuit voltage are discussed. In addition to the intrinsic effect an extrinsic photovoltaic effect was found. Arguments are given to show that the extrinsic response is not an electrode effect, but is clearly correlated with the specific dope introduced into the GaP bulk.