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We report a positron annihilation study using state-of-the-art experimental and theoretical methods in n-type and semi-insulating β - Ga 2 O 3. We utilize the recently discovered unusually strong Doppler broadening signal anisotropy of β - Ga 2 O 3 in orientation-dependent Doppler broadening measurements, complemented by temperature-dependent positron lifetime experiments and first principles calculations of positron-electron annihilation signals. We find that split Ga vacancies dominate the positron trapping in β - Ga 2 O 3 single crystals irrespective of the type of dopant or conductivity, implying concentrations of at least 1 × 1 0 18 c m - 3.

It has been established that hydrogen (H) plays a key role in p-type doping of GaN and it must be removed by dissociation of the Mg–H complex in order to achieve p-type conductivity. However, in carbon (C)-doped semi-insulating GaN, which is the core component of power electronic devices, the role of H, especially the formation and dissociation process of C–H defects, has remained to date a mystery. In this work, we provide a direct evidence for the interaction between H and C in the form of the C N − H i complex in as-grown C-doped GaN. The complex can be dissociated into C N − and H + after post-growth annealing. The activation energy is estimated to be about 2.3–2.5 eV from the temperature-dependent annealing experiments. Our study reveals that the C N − H i complex plays an essential role in understanding the variation of optical and electronic properties of C-doped GaN.

Cathodoluminescence investigations on bulk undoped semi-insulating GaAs samples taken from different sources reveal the presence of a deep level emission at 0.9 eV at 77 K, with a narrow full width at half maximum of 8 meV. The temperature-dependent and beam-parameter-dependent studies indicate that, the probable origin for this emission may be some nanocluster/quantum-dot like structures with a band gap of 0.9 eV, present inside the semi-insulating GaAs crystal lattice. One possibility for such structures in semi-insulating GaAs are clusters/nanoprecipitates of arsenic.

Quenching effects induced by additional below-bandgap illumination in undoped semi-insulating GaN were investigated using optical admittance spectroscopy (OAS) and photocurrent (PC) spectroscopy as well as optically excited, thermally stimulated currents (TSC). In OAS and PC, a decrease of defect-related signals due to the quenching light was observed. The thermal quenching of the defect band between 2.7 and 3.3 eV shows a good agreement with thermal emissions as measured by TSC, indicating the same defects cause the optical transitions in OAS/PC and the thermal transitions in TSC. The thermal emission in the temperature region between 250 and 300 K, which is responsible for the thermal quenching of the blue band (BB) in OAS, also shows an optical quenching under below-bandgap excitation.

Surface photovoltage spectroscopy (SPS) studies on thick semi-insulating (SI) GaAs wafers have been done in the range 800–1100 nm using chopped light geometry. SPS peaks at 880 nm, 900 nm, and a broadband in the range 930–1080 nm have been observed. These observations are important as SPS is routinely used to study absorption-related features in InAs self-organized quantum dots grown on SI GaAs. The effect of the ambient and chopping frequencies on SPS spectra is also presented.

We have determined the capture and emission coefficients by EL2 traps in semi-insulating n-GaAs using available experimental results. To this end, we have derived a simplified mathematical model from the complete drift–diffusion equations by singular perturbation methods. The capture and emission coefficients are adjusted so that the numerically obtained steady-state and high-field charge dipole solutions of the simplified model match the available experimental results.

Iron doping of InP and GaInAsP(λg=1.05 μm) layers grown by metalorganic molecular beam epitaxy was studied using elemental source material in combination with a conventional effusion cell. This study was aimed at the creation of semi-insulating optical waveguides under growth conditions compatible with selective area growth. Secondary ion mass spectroscopy measurements revealed a reproducible and homogeneous incorporation behavior of the iron dopant in the materials investigated. Resistivities in excess of 109 Ω cm were obtained for both compositions at medium doping levels. GaInAsP/InP waveguide structures grown at 485 °C—the minimum temperature necessary for selective deposition—exhibited averaged resistivities of 5×107 Ω cm in combination with optical losses of 2.5±0.5 dB/cm.

The temperature dependence of the terahertz (THz) output power and spectra from biased photoconductive switches was measured for several antenna gap widths and applied biases. The spectrally integrated THz output had a nonmonotonic temperature dependence in all cases with the value increasing by a factor of 3 from room temperature to 150 K for low biases and 100 K at high biases. An abrupt decrease in output power occurs below 90 K, and the spectrum shifts to lower frequencies as the temperature is lowered.

The temperature dependences of the optical absorption edges of semi-insulating GaAs and InP have been measured from room temperature to 905 °C and 748 °C, respectively, with accuracies of ±1 °C at room temperature and ±5 °C at 900 °C. The temperature dependence of the optical absorption edge is adequately reproduced by an Einstein model although the Varshni model gives an improved fit to the band gap. Finally, the widths of the absorption edges are correlated with ionicity.

A model of the temperature behavior of the photoquenching of EL2 in semi-insulating GaAs is presented. The thermal emission of a hole trapped on an actuator level accounts for the very low photoquenching efficiency above 85 K. This effect is presented in terms of a set of rate equations that reproduce in a reliable way the temperature dependence of the photoquenching of EL2. The activation energy of the actuator level suggests a hole trap level other than GaAs as was previously assumed.

The influences of microdefects and dislocations on the lattice parameters of undoped semi‐insulating GaAs single crystals were analyzed, and a novel nondestructive method for measuring stoichiometry in undoped semi‐insulating GaAs was established in this letter. The comparison of this method with coulometric titration indicates that the method of nondestructive measurements is indeed convenient and reliable.

Vanadium ion (V+) implantation has been successfully applied to the formation of semiinsulating 6H‐SiC layers. The resistivity of V+‐implanted layers strongly depended on the conduction type of initial 6H‐SiC crystals. The resistivity at room temperature exceeded 1012 Ω cm and 106 Ω cm for p‐ and n‐type samples, respectively. Compensation mechanism is discussed based on the temperature dependence of resistivity. This technique will be useful for device isolation, edge termination, and reduction of parasitic impedance of SiC devices.

Electrical homogeneity is an essential requirement for semi‐insulating (SI)InP:Fe wafers. A method is presented to measure the spatial distribution of resistivity at room temperature via the photorefractive effect. The experimental conditions are presented and discussed. The potential of the method is demonstrated by applying it to SI liquid encapsulated Czochralski grown material.

Detailed experimental results are presented for a ‘‘thermal quenching’’ of thermal stimulated current signals in the most prominent trap in undoped semi‐insulating (SI) GaAs, T5 with an activation energy of 0.27–0.31 eV. A possible model for the thermal quenching of T5 is discussed, emphasizing the thermally stimulated nature of the quenching process, the effect of electric field and the formation of high‐field domains. The thermal quenching of T5 can frequency be observed in SI GaAs grown by the vertical gradient freeze (VGF) technique, or by the liquid encapsulated Czochralski (LEC) technique under certain conditions.

We show that positron trapping at negative As vacancies revealed under illumination in bulk semi‐insulating GaAs correlates with a form of near‐band‐edge absorption known as reverse contrast (RC). We conclude that it is the ionization of As vacancies to their negative charge state that gives rise to RC absorption.

Electroluminescence (EL) and photoluminescence have been measured from thin film structures of heavily carbon‐doped GaAs on crystalline semi‐insulating GaAs substrates. EL is only detected when the p‐type film is biased positively. From this and the spectral distribution, it is concluded that there are heterojunction interface states at about 50 meV below the conduction band, with a concentration roughly estimated as 1017 cm−3.

Electric‐field domains in semi‐insulating GaAs:Cr are investigated both by imaging the locally induced birefringence using a transverse electro‐optic configuration and by measuring the dc current flowing through the crystal. It is shown that the formation of domains may be controlled by optical means.

Photoinduced current transient spectroscopy has been used to show the effect of thermal annealing on deep level defects in semi‐insulating Fe doped InP wafers. The annealing experiments have been accomplished in an infrared image furnace during 15 min at temperatures ranging from 663 to 820 °C. We show that this treatment leads to the formation of four deep traps named T1–T4 having the following activation energies: 0.14, 0.21, 0.41, and 0.53 eV, respectively. We show that the thermal anneal at high temperature leads to deterioration of the electrical properties of the material.

A combination of a lateral n‐p‐n junction using an amphoteric doping of Si in GaAs and a semi‐insulating GaAs grown at low temperature is applied for the first time to a novel current confinement structure for an index‐guided InGaAs strained quantum well laser grown by two‐step molecular beam epitaxy. A threshold current of 7.4 mA and total external differential quantum efficiency of 59% under room temperature continuous wave operation are achieved with devices fabricated by a self‐aligned process.

A new type in‐plane gated field effect transistor where the semi‐insulating substrate itself is used as a gate insulator region is proposed. n‐ and p‐type in‐plane gated field effect transistors are fabricated on a semi‐insulating GaAs substrate by focused ion beam scanning of Si++ and Be++, respectively. These in‐plane gated field effect transistors are found to operate well at room temperature.

The optically induced EL2*‐EL2 transformation is studied by photocurrent measurements, allowing the monitorization of the free‐carrier generation during the near‐band‐gap (NBG) recovery excitation. The efficiency recovery spectrum is found to be anticorrelated with the NBG photocurrent spectrum. This observation rules out the possibility of a free‐carrier assisted process as the main mechanism accounting for the NBG induced EL2*‐EL2 reverse transformation.

We report the first observation of the photorefractive effect in cadmium sulfide at low optical power. The maximum gain coefficient measured with no applied field at 633 nm is 0.3 cm−1. The response time scales sublinearly with intensity and is independent of grating spacing. At a maximum intensity of 80 mW/cm2, a response time of 0.9 ms is obtained. The photorefractive sensitivity is the largest among photorefractive material operating in the visible range.

Undoped semi‐insulating (SI) InP wafers were obtained by high‐temperature annealing under high phosphorus over pressure. These wafers show resistivities higher than 107 Ω cm, with mobilities greater than 4000 cm2 V−1 s−1. The SI properties could be held even after cap annealing with SiNx films at 700 °C for 15 min. The activation energy of deep levels causing the semi‐insulation was estimated as 0.64 eV. Photoluminescence measurements made on undoped SI InP show hitherto unknown peaks in the long wavelength region between 1000 and 1400 nm.

Processes induced by below-the-gap illumination and related to defects having deep levels in liquid-encapsulated Czochralski semi-insulating GaAs crystals were studied. It was found that the dynamics of both optical quenching and thermal recovery (above 125 K) of thermally stimulated current signal related to six deep traps was the same as that of the EL2 related photoconductivity signals. Analysis of these results gives evidence that some of the observed deep traps in GaAs are complex defects, which might include as their constituent the EL2 defect. It means that EL2 could serve as a gettering center for other native defects and/or impurities. The proposed model is in accordance with other recently published results associating several deep traps (EL6, EL3, EL5, and EL14) with EL2 (29 References).

Suppression of the Schottky barrier effect in semi‐insulating GaAs is demonstrated by centering the pump irradiation on the reverse bias crystal‐electrode interface. A photorefractive gain coefficient Γ of 2.7 cm−1 is achieved. The irradiation suppression overcomes the need for externally applied ohmic contacts.

We report the observation by photoluminescence of the gallium antisite double acceptor in As‐rich GaAs grown by the liquid‐encapsulated Czochralski technique. In the semi‐insulating material both arsenic antisite and gallium antisite defects are present simultaneously which must be taken into account for any electrical compensation model.

Electron paramagnetic resonance was used to study semi-insulating (SI) 4H-SiC substrates doped with vanadium (V) in the range of 5.5× 1015 -1.1× 1017 cm-3. Our results show that the electrical acti ...

By using combination of detailed experimental studies, we identify the metastable and stable energy levels of EL2 in semi-insulating GaAs. These results are discussed in the light of the recently proposed models for stable and metastable configurations of EL2 in GaAs.

Complex changes in the distribution of thermally stimulated current peaks with illumination time and intensity are reported for a sample of semi‐insulating GaAs. With weak illumination for 5 sec, at least six peaks were seen, while after a 1‐min illumination only four peaks were evident. With stronger illumination, the thermally stimulated current essentially consisted of two major peaks, at about 115°K and 278°K. The 115° peak first increased with illumination time, passed through a maximum, and was quite small after a 12‐hr illumination, while the 278° peak became very large.

In conjunction with studies relating to high‐power CO2 laser windows the linear absorption coefficient α of Cr‐doped GaAs was measured by means of calorimetric techniques. It was found that α ≈ 0.02 cm−1, at room temperature. This result is shown to be consistent with theoretical considerations: At 10.6 μ, the lattice absorption of GaAs stems from the existence of a fourth‐order electric moment and does not involve the fundamental resonance.

A new technique for recording spatial fluctuations of the optical absorption in GaAs slices is reported. It is based on a commercially available linear silicon diode array which monitors the optical absorption attributed to the omnipresent deep trap named EL2. Because this technique gives quantitative results, displays excellent spatial resolution (200 μm for 2‐in. wafers), and is fast, it appears to be highly useful for wafer characterization and quality control.

We report ballistic phonon experiments in semi‐insulating GaAs as a function of polarization and propagation direction and of the concentration of chromium in the crystal. The data provide direct evidence for a tetragonally distorted site symmetry of the Cr ions and a ground‐state splitting at ∼14 K.

Bulk, undoped, semi‐insulating, liquid encapsulated Czochralski GaAs crystals have been annealed under controlled arsenic pressures, and the uniformities of EL2 concentration and resistivity were investigated. Crystals were grown from different melt compositions from Ga rich to As rich. Arsenic pressure was changed from 0 (vacuum) to 3.4×103 Torr. As a result, it was found that both EL2 concentration and resistivity in the crystal grown from As‐rich melt have the lowest fluctuations around 530 Torr arsenic pressure.

Deep level photoluminescence (PL) associated with the dominant midgap donor EL2 in semi‐insulating (SI) GaAs crystals has been observed for the first time at room temperature. A broad emission band with a peak at 0.65 eV was observed always in commercial undoped SI GaAs wafers. The association of the 0.65 eV band with the EL2 level has been verified on the basis of the semiquantitative agreement of the distribution on wafers between the PL intensity and the EL2 absorption. Room‐temperature PL spectroscopy can be used as a powerful tool to investigate the nonuniformity of the EL2 distribution on commercial wafers with a high spatial resolution.

The cathodoluminescence (CL) imaging technique is applied to the characterization of semi‐insulating GaAs substrates after an extrinsic gettering treatment. A reverse contrast CL image is found for the gettered material. This study provides evidence for the physical mechanism taking place in the gettering process and contributes to the understanding of the effect of dislocations on device performance.

Crystal homogeneities in liquid‐encapsulated Czochralski grown, semi‐insulating GaAs (100) wafers were evidently improved by annealing at 800 °C for more than 12 h. The improvement was confirmed by observing cathodoluminescence intensity line scanning profile and by measuring field‐effect transistor (FET) threshold voltage standard deviation σVth. σVth for 14‐h and 18‐h annealed/polished wafers exhibited about one‐half that for a nonannealed wafer. Direct evidence of the improvement was also obtained by measuring dislocation effect on FET threshold voltage.

Charge carrier transport in thermally converted surface layers in semi‐insulating GaAs depends on the generation, diffusion, and occupancy of Ga and As vacancies. The amphoteric nature of C in GaAs can significantly alter the density and the distribution of donors and acceptors in the vicinity of the specimen surface and the surface layer may become either p type or n type depending on the thermal treatment conditions.

Oxygen concentration in a horizontal Bridgman‐grown, chromium and oxygen‐doped, semi‐insulating GaAs ingot was analyzed using charged particle activation analysis. The oxygen concentration ranged from 2.0×1015 at seed end to 7.2×1015 cm−3 at tail end. The change of oxygen concentration measured along the length of ingot was in accordance with the normal‐freeze equation. The effective distribution coefficient of oxygen was estimated to be 0.39.

Miyazawa et al. [Appl. Phys. Lett. 43, 853 (1983)] have recently established a spatial correlation between variations in field‐effect transistor performance and nonuniformities in the cathodoluminescence (CL) efficiency of semi‐insulating (SI) GaAs substrates. In this study, we compare the CL uniformity of both Cr‐doped and undoped SI GaAs crystals grown by the liquid‐encapsulated Czochralski (LEC) technique with undoped SI crystals grown by the horizontal gradient freeze (HGF) technique. In contrast to the LEC crystals, HGF GaAs has extremely uniform CL characteristics which should result in uniform device performance.

A significant improvement in the maximum output power of a 1.3 μm GaInAsP/InP laser with a semi‐insulating current confinement structure is reported. The improvement has been achieved by interposing an n‐type InP layer between a p‐InP substrate and an Fe‐doped InP layer. A maximum cw output power of 180 mW and a modulation bandwidth of 8.5 GHz have been obtained.

A high spatial resolution, near infrared absorption method has been used to determine [EL2] concentrations in semi‐insulating undoped Czochralski liquid encapsulated (LEC) GaAs. Fine structure superimposed on the well‐known ‘‘W’’ distribution across 〈110〉 diameters of {001} wafers has been detected. Fine structure has also been directly observed in {110} sections of ingots grown along 〈001〉 using a CCTV vidicon system to observe transmitted infrared radiation. The structure consists of narrow bands of increased absorption which correspond with high densities of dislocations in the same specimens.

We present experimental evidence for the presence in semi‐insulating undoped GaAs of the double‐acceptor defect with ionization energies of 78 and 203 meV, which is currently attributed to the GaAs antisite in concentrations of at least 2×1015 cm−3. We then discuss the implications of this result for the compensation mechanism in these materials.

A new quantitative photoelastic method has been developed to measure residual strains in undoped semi‐insulating (001) GaAs substrates for integrated circuits. The absolute values of the shear strain ‖exy‖ and the difference of the expansion and contraction strains ‖eyy−exx‖ existing in the (001) substrate plane are quantitatively determined by using the present method. Their two‐dimensional distribution maps are demonstrated to exhibit fourfold symmetries rotating 45° to each other. The absolute values are found to be of the order of 10−5 at the substrate edges.

Electron paramagnetic resonance studies on as‐grown semi‐insulating liquid encapsulation Czochralski (LEC) GaAs at 35 GHz have revealed a new resonance labeled FR3. It is consistently present in LEC material but usually unobservable in Bridgman samples, thus strongly indicating that the defect involved contains boron. The center has trigonal symmetry and is electrically active. Its spectrum indicates a d 9 or p5 one‐hole configuration. We tentatively identify FR3 with a Ga antisite complex, Ga−As ‐B0Ga.