N-type GaP Research Articles

Wafer bonding with low-temperature-grown (Ga,P) as an adhesive material

Amorphous and polycrystalline (Ga,P) grown with the molecular beam epitaxy technique at low temperatures were developed as adhesive materials for wafer bonding technology. The microstructure and V/III incorporation ratio in (Ga,P) were studied with transmission electron microscopy (TEM) and Auger electron spectroscopy. The crystallinity of the low-temperature-grown (LTG) (Ga,P), amorphous or polycrystalline, is controlled by the phosphorus overpressure during growth. The n-type GaP substrates, each with LTG (Ga,P) material on top, were strongly bonded face-to-face at 600 °C for several hours. TEM shows that along the bonded interface recrystallization of the (Ga,P) layer has taken place during high-temperature annealing and hence helped the two wafers bond together. In comparison, direct wafer bonding of GaP substrates without LTG (Ga,P) requires high bonding temperatures above 750 °C. The current–voltage (I–V) characteristics of the bonded samples were also investigated. Samples bonded with Ga-rich polycrystalline (Ga,P) exhibit linear I–V dependence across the bonded interface. In contrast, samples bonded with P-rich amorphous (Ga,P) show back-to-back Schottky I–V characteristics with a breakdown of about 11–13 V. The two bonded interfaces show great similarity in microstructure except that gallium clusters are present only at the interface of the sample bonded with Ga-rich polycrystalline (Ga,P). We attribute the linear ohmic I–V dependence to the presence of Ga-clusters.

Nonstoichiometric deep levels in Mg-doped GaP epitaxial layers

We have investigated the relation between deep levels in Mg-doped p-type GaP liquid phase epitaxy (LPE) layers and stoichiometry of the surface of the substrates by PHCAP measurement. Concentration of a deep donor level at E C−1.9–2.1 eV is higher in an n-type undoped GaP substrate annealed with applying phosphorus vapor pressure of 20 kPa than in sample annealed beneath a carbon cover. Next, Mg-doped LPE layers are grown on substrates that have been pre-annealed under phosphorus vapor pressure just before the growth. The densities of deep levels at E V+0.85 and E V+1.5 eV in long-time (2 h) pre-annealing sample are greatly decreased, but a deep level at E C−1.9–2.1 eV shows opposite tendency. The latter is thought to be identical to a deep level detected in the substrate, probably phosphorus interstitial atoms.

Influence of defects on the formation of thin porous GaP(001) films

The results are presented of the optical and X-ray studies of the structure of n-type subsurface GaP(001) layers implanted with 300 keV-He+-(D = 1016 at./cm2) and 600 keV-Xe2+-ions (D = 1012 at./cm2) and then subjected to electrochemical anodizing in aqueous 0.25 M H+ solution. It is shown that defects formed in the crystal lattice as a result of this treatment considerably influence the character of electrochemical etching and the structural parameters of the formed layers. It is shown that anodic etching proceeds over the defects, which allows one to obtain oriented systems of pores by choosing the appropriate conditions of preliminary implantation.

Hot carrier luminescence during porous etching of GaP under high electric field conditions

Electroluminescence is observed during porous etching of n-type GaP single crystals at strongly positive potential. The emission spectra, which include a supra-bandgap contribution, are markedly different from the spectra observed under optical excitation or minority carrier injection. The current density and electroluminescence intensity show a strong potential dependence and a similar hysteresis. The spectral characteristics of the luminescence suggest that both thermalised and hot charge carriers, generated by impact ionisation, are involved in light emission.

Formation of Whiskers at Dislocation Sites of n-Type GaP Surface during Anodic Etching

It was recently found that the electrochemical dissolution of an n-GaP (111) surface proceeded selectively or uniformly in an aqueous KOH solution, depending on an anodic high-voltage above ten volts. In the present study we report the formation of whiskers at dislocation sites of the n-GaP (111) surface that remain undissolved at an anodic voltage of 16 V in the 0.5 kmol·m−3 KOH solution.

A comparative study of semiconductor sensitization by micro-crystals of indium sulfide on various porous wide band gap semiconductor substrates

Semiconductor sensitization on various n-type wide band gap semiconductors was studied by micro-crystals of n-type indium sulfide. The generation of an anodic photocurrent on the electrode is explained from the viewpoint of semiconductor sensitization. A very high incident photon-to-current conversion efficiency (IPCE) of more than 80% was achieved on In2S3/In2O3 electrodes in a polysulfide electrolyte. The observed values for the IPCE for In2S3/TiO2 and In2S3/ZnO electrodes were rather low compared to that of In2S3/In2O3 electrodes, in the same electrolyte. The semiconductor sensitization process was not observed on In2S3/ZnS electrodes. Different kinetics at the semiconductor/semiconductor interface are the reasons for the observed difference of the IPCE, for the electrodes.

Field emission from porous (100) GaP with modified morphology

Morphology of n-type porous GaP samples with (100) crystal orientation was modified by postchemical etching for field-emitter application. The structures produced have uniform size and shape distribution and are found to show good emission characteristics. The mechanism of the morphology modification is explained, and a strong correlation between field-emission characteristics and postchemical etching time is shown.

Electrical and Optical Properties of Chromium Doped GaP

The electrical properties of p-type GaP:Cr:Zn and n-type GaP:Cr:S samples have been studied using Deep Level Transient Spectroscopy (DLTS). In GaP:Cr:Zn a deep hole emitting level is detected with a thermal activation energy of Ev + 0.48 eV and attributed to the Cr3+/4+ donor level of substitutional CrGa. In GaP:Cr:S a deep electron emitting level is detected at Ec — 0.30 eV and attributed to the Cr+/2+ double acceptor level of CrGa. The emission rates of both levels are found to be electric field dependent which can be fitted by a Poole-Frenkel model. Deep Level Optical Spectroscopy (DLOS) measurements were performed on both levels in the filled as well as in their emptied state. The Frank-Condon shifts were estimated from these measurements. The spectral shape of these DLOS spectra is discussed as due to photoionization transitions.

Large magnetoresistance in double perovskite Sr 2Cr 1.2Mo 0.8O 6-δ

Sr 2Cr 1.2Mo 0.8O 6-δ (δ=0, 0.2) with a double perovskite structure was prepared by solid state reaction in evacuated quartz tubes. Cr and Mo are partially ordered on the B site. Oxygen vacancies decrease the ordering, but increase the lattice parameters. X-ray absorption spectroscopy results are consistent with Cr being 3+, and Mo being close to 5+ for δ = 0.2 and 5.5 for δ = 0. The spin of Cr 3+ (d 3) and Mo 5+ (d 1) order in an anti-parallel arrangement by superexchange interaction, and lead to ferrimagnetic ordering below 465 K. Both compounds are n-type narrow gap semiconductors. Large magnetoresistance (-43%) is observed in Sr 2Cr 1.2Mo 0.8O 6. The MR behavior is attributed to an intra-grain tunneling mechanism.

A highly UV-selective Schottky-barrier photodiode based on a Ag–GaP contact

A Schottky-barrier photodiode with spectral sensitivity in the 300–340 nm region has been prepared successfully using the transmission window of silver and its barrier effect on GaP. Radio-frequency magnetron sputtering has been used for deposition of the silver film. Silver films with thicknesses in the 10–150 nm range exhibit a transmission window at a wavelength of about 320 nm, which can be used as an ultraviolet (UV) bandpass on a GaP photodiode. Furthermore, the Schottky contact of sputtered silver films on n-type GaP grown by liquid-phase epitaxy shows good characteristics, including large barrier heights (1.2–1.3 eV) and low reverse currents (below 2 pA cm−2 at 5 V). The GaP photodiode with a silver Schottky contact exhibits a sensitivity of 0.02 A W−1 at a wavelength of 320 nm. The simplicity of this structure of a UV sensor opens up the possibility for mass production.

Short wavelength bottom-emitting vertical cavitylasers fabricated using wafer bonding

Selectively oxidised 850 nm vertical cavity surface emitting laser diodes which emit through transparent n-type GaP and AlGaAs substrates are reported. The short wavelength bottom-emitting lasers are fabricated using a low temperature inert gas wafer fusion process. Compared to top-emitting lasers, the bottom-emitting lasers bonded to n-type AlGaAs substrates show comparable electrical characteristics, while lasers bonded to n-type GaP substrates exhibit higher series resistance and voltage.

Ion implantation as a tool for controlling the morphology of porous gallium phosphide

We investigate the morphology of porous layers obtained by electrochemical anodization of (100)-oriented n-type GaP substrates before and after a preliminary 5-MeV Kr+ implantation. Apart from favoring the observation of a surface-related phonon in the frequency gap between the bulk optical phonons, ion implantation appears to be an effective means of controlling the morphology of porous GaP, irrespective of initial substrate material features.

Characteristics, behavior, and identification of electron-induced defects in GaP

The mechanism by which minority-carrier injection induces annealing of the defects created by electron irradiation in n-type GaP has been revisited. For this a precise determination of the energy levels of electron traps, that are observed to anneal, has been made. The annealing kinetics have been monitored versus temperature and injection density. They demonstrate that the mechanism that was originally proposed to explain the injection annealing, namely, that the activation energy for thermal annealing is decreased by a quantity equal to the energy released by hole trapping, cannot apply. Another mechanism is proposed, which has been found to apply in GaAs, to fit quantitatively the experimental results. According to this mechanism, injection annealing is athermal, and induced by alternative captures of electrons and holes on the defect site.

PdIn contacts to n-type and p-type GaP

PdIn was used as a contact material to n-type and p-type GaP. On n-type GaP it forms a low resistance ohmic contact upon rapid thermal annealing. PdIn/n-GaP (S doped at 2–3 ×1018 cm−3) contacts annealed at 600 °C for 1 min had specific contact resistance’s lower than 1×10−4 Ω cm2. Unlike the contacts to n-GaP, PdIn contacts to p-GaP (Zn doped 1–2×1018 cm−3) show rectifying behavior at all annealing conditions. However, the effective Schottky barrier height seems to decrease significantly with thermal annealing. In addition to the electrical measurements, glancing angle x-ray diffraction was used to characterize the contacts. The glancing angle x-ray diffusion pattern of PdIn/n-GaP, annealed at 600 °C for 1 min, is consistent with the formation of an (InyGa1−y)P phase due to the thermal annealing. The ohmic behavior of the PdIn contacts to n-type GaP and the decrease in the contact’s Schottky barrier height on p-type GaP is attributed to the formation of this (InyGa1−y)P phase at the contact’s interface.

The origin of blue and ultraviolet emission from porous GaP

The luminescence properties of porous n-type GaP are reported. Apart from the orange emission of bulk GaP, emissions in the blue and ultraviolet are observed. Evidence is presented to show that this blueshifted emission is not due to quantum confinement effects, as previously suggested, but to gallium oxide on the surface of the porous material.

Features of radiative transitions of charge carriers in Al x Ga1−x As and GaAs x P1−x p-n-structures

The AlxGa l_xAs and GaAsxPi-x compounds have formed the basis for the development of highly efficient light-emitting diodes for the visible and IR regions of the spectrum. The position of the edge luminescence band in these materials is controlled by the quantity x without a noticeable change in the efficiency of electroluminescence (EL). The losses occurring in this case are caused not only by radiationless transitions of nonequilibrium carriers, but also by rec. mbination in an undesirable spectral regior,. B~I ..... we present results that reveal such a channel of recombination and indicate that under certain conditions its role in the occurring processes can be substantial. We also investigated the EL spectra with reverse-biased diode structures, which indicate the dominant role of hot carriers in the formation of such radiation. The objects of investigation were epitaxial AlxGat-xAs and and GaAsxPl-x p-n structures�9 The layers of AIxGal-xAs of the n- and p-types were obtained by the method of liquid epitaxy on GaAs substrates with a hole concentration of about 1018 cm -3. The width of the forbidden band Eg in the p-type AI0.1sGa0 8sAs layers was 1.66 eV at 300 K, and the hole concentration in it was equal to about 5.1017 cm -3. The n-type AIo4Ga0.6As layers h;ad a large fordidden band (1.95 eV, 300 K), while ~hc electron concentration was close to 2-1018 cm -3. Mesa diodes with an area of 0.4  0.4 = 0.16 mm 2 were formed by chemical etching in a 5H2SO4:2H202:IH2 0 solution at 75-80~ [1 ] using photolithography. Ohmic contacts with both n- and p-regions were created by chemical deposition of Au-Ni-Au with subsequent burning in a flow of dried hydrogen at 420-450~ The lateral and frontal surfaces of the mesa structures were protected by dielectric layers of A1203 and SiOz obtained by pyrolytic deposition in a vacuum chamber. The n-type GaAsxPI-x layers (x = 0.15, Eg = 2.18 eV at 300 K~, which were doped with tellurium up to 1015-1016 cm -3, were obtained by gas-phase epitaxy on n-type GaP substrates with a carrier concentration of 1016-1017 cm -3. The p-n junct,ons were produced by zinc diffusion (to a concentration of 10 )8 cm -3) into an epitaxial n-layer. The use of an Au-Bi (2~o) alloy for ohmic contacts made possible chemical etching of the diodes (in a 3H2SO4:iH202:IHz O solution at 60~ to remove the disturbed laver on the side surface of the p-n-junction after mechanical cutting of the wafer into diodes measuring 0.4  0.4 mm ]2 1. We performed spectral measurements on a setup consisting of a double quartz monochromator with a photomultiplier (1.7-4.0 eV) and a cooled PbS photoresistor r eV) as detectors. The setup was carefully calibrated for spectral sensitivity by a certified tungsten ribbon lamp. Figure 1 presents the spectra of injection EL for the p-n structures under investigation with forward bias. The characteristic feature of these spectra is the presence of wider-band radiation in the IR region (hv < 1.8 eV) along with a dominating shortwave band in the visible spectrum region. As we can see from Fig. 1, the contribution of the IR band to the total radiation of the AlxGa l_xAs p-n heterostructure changes substantially depending on

Band bending within inhomogeneously doped semiconductors with multilevel impurities. II. Examples.

Using the method for calculating the band bending and concentration profiles of a multilevel impurity center in its different charge states within a semiconductor inhomogeneously doped with the impurity proposed in the preceding paper [X. Yang et al., Phys. Rev. B 53, 13 414 (1996)] to n-type GaP implanted with Ni and Fe ions, respectively, the results were obtained for the samples implanted and annealed under different conditions. Based on the results, a feasible explanation of the deep-level transient spectroscopy spectra of Ni ion-implanted n-type GaP was obtained and an analysis for the M\"ossbauer spectra of Fe ion-implanted n-type GaP was carried out. \textcopyright{} 1996 The American Physical Society.

Improved contact resistance to n-type wide gap II–VI semiconductors

The Schottky barrier at AlZn1−xCdxSe junctions was determined through high resolution synchrotron radiation photoemission studies of interfaces fabricated in situ on atomically clean, Se-rich surfaces. A gradual decrease in the n-type barrier with increasing x reflects the bandgap variation in the ternary alloy and the band alignment in Zn1−xCdxSeZnSe heterojunctions. Correspondingly, transport studies of Aln-Zn1−xCdxSe contacts fabricated ex situ show a dramatic decrease of the specific contact resistance with increasing x. Improved performance of Aln-ZnSe contacts can therefore be achieved through fabrication of graded Zn1−xCdxSe layers at the interface.

On the increase of the photocurrent quantum efficiency of GaP photoanodes due to (photo)anodic pretreatments

It has been found that the photocurrent quantum efficiency of n-type GaP single crystal electrodes illuminated with visible light (green-blue) increases markedly as a consequence of photoanodic etching or polarization at very positive potentials. The origins of this increase have been systematically investigated. Two effects are of importance. Photoanodic etching leads to a roughening of the surface; as a consequence the incident light is scattered and absorbed more effectively in the region of the solid in which electron-hole pairs are separated by diffusion or migration. In addition, photoanodic current flow or severe positive polarization lead to a considerable increase of the diffusion length of the photogenerated holes. This effect is attributed to passivation of hydrogen-related recombination centers by hole capture and subsequent release of hydrogen.

Schottky diode properties of Au, InGaP (111) and (110) chemically etched surfaces

n-Type GaP (111) and (110) surfaces etched with bromine-methanol 1% or H 2SO 4, H 2O 2, H 2O (3,1,1) have been studied by Auger electron spectroscopy. From this study we concluded that there is less oxide on a surface etched with the second solution. (Au) (In)/GaP schottky diode have been made by evaporating Au and In dots. Characteristic properties of these diodes, obtained from I( V) or C( V) measurements, have been compared. From this comparison, it becomes clear that the diode characteristics depend on the surface contamination, on the residual oxide layer and on the metal. The role of the surface structure, the contamination and the metal have been deduced.