CV Profiling Research Articles

Precision calibration of the silicon doping level in gallium arsenide epitaxial layers

An approach to precision calibration of the silicon doping level in gallium arsenide epitaxial layers is discussed that is based on studying the dependence of the carrier density in the test GaAs layer on the silicon- source temperature using the Hall-effect and CV profiling techniques. The parameters are measured by standard or certified measuring techniques and approved measuring instruments. It is demonstrated that the use of CV profiling for controlling the carrier density in the test GaAs layer at the thorough optimization of the measuring procedure ensures the highest accuracy and reliability of doping level calibration in the epitaxial layers with a relative error of no larger than 2.5%.

Shielded hydrogen passivation − A potential in‐line passivation process

Shielded hydrogen passivation (SHP) is a recently developed technique for introducing atomic hydrogen into materials and it offers significant advantages over the other hydrogenation techniques. Hydrogen de‐activation of boron followed by electrochemical CV profiling was used to demonstrate that substantial quantities of atomic hydrogen can permeate though palladium/silver alloy foils which are 10 µm thick. It is thought that such thickness will be sufficient to withstand pressures of up to 1 atmosphere allowing passivation in an in‐line process. Further, it is shown that poisoning of the foil by using sulphur increases the flux of atomic hydrogen released. SHP delivers extremely good passivation of SiO2‐Si interfaces, as demonstrated by using thermally oxidised 1 Ω‐cm, n‐type silicon where the lifetime, at 1015 cm−3 injection level, was found to increase from 12 to 1.05 ms after SHP processing. Upon application of corona charge, the lifetime further increased to 6.3 ms, equivalent to SRV ≤ 0.17 cm s−1.

Vacancy Clusters in Germanium

Fast neutron irradiation of germanium has been used to study vacancy reactions and vacancy clustering in germanium as a model system to understand ion implantation and the vacancy reactions which are responsible for the apparently low n-type doping ceiling in implanted germanium. It is found that at low neutron doses (~1011cm-2) the damage produced is very similar to that resulting from electron or gamma irradiation whereas at higher doses (> 1013cm-2) the damage is similar to that resulting from ion implantation as observed in the region near the peak of a doping implant. Electrical measurements including CV profiling, spreading resistance, Deep- Level Transient-Spectroscopy and high resolution Laplace Deep-Level Transient-Spectroscopy have been used in conjunction with positron annihilation and annealing studies. In germanium most radiation and implantation defects are acceptor like and in n-type material the vacancy is negatively charged. In consequence the coulombic repulsion between two vacancies and between vacancies and other radiation-induced defects mitigates against the formation of complexes so that simple defects such as the vacancy donor pair predominate. However in the case of ion implantation and neutron irradiation it is postulated that localized high concentrations of acceptor like defects produce regions of type inversion in which the vacancy is neutral and can combine with itself or with other radiation induced acceptor like defects. In this paper the progression from simple damage to complex damage with increasing neutron dose is examined.

Analysis of tellurium as n-type dopant in GaInP: Doping, diffusion, memory effect and surfactant properties

The use of tellurium as n-type dopant for GaAs and InP has several advantages, including a high incorporation efficiency, the very high doping levels achievable and a low diffusion coefficient. However, its use to dope Ga x In 1− x P is not straightforward, since it shows several problems like a remarkable memory effect and an acute inertia of the material to become Te-doped, which gives rise to gradual doping profiles. In this paper, all these phenomena are studied and quantified using secondary ion mass spectroscopy (SIMS) and electrochemical CV profiling (ECV) measurements. Concerning the gradual doping profiles, their origin is linked to the interaction of Te and In in the gas phase and on the growth surface. A phenomenological explanation is given for this effect although the exact physical processes behind remain to be defined.

Clinical, biochemical and cardiovascular implications of endothelial dysfunction in the dermal microcirculation

Endothelial dysfunction (ED) might be an important and early event in the pathogenesis of major cardiovascular diseases. AIMS: 1.To determine the prevalence of abnormal endothelium-dependent vasodilation (EDV) 2.To assess its correlation with clinical, biochemical, inflammatory and extracellular matrix (ECM) activity markers. 3.To determine its correlation with ambulatory blood pressure monitoring (ABPM) and cardiovascular characteristics. N=121, aged 22-81(58,34+-1,28), 48,7%M, 77hypertensives, BMI (kg/m2) waist (cm).Gly, creat, HDL, LDL, chol, and tg, by Hitachi. IR-HOMA score. ECM: COMP (Cartilage Oligomeric Matrix Protein)(AnaMar EIA)(U/L).CRPhs: DRG EIA.(mg/L). ABPM: Spacelabs 90210: Systolic BP, Diastolic BP, and Mean Arterial Pressure MAP((SBP-DBP/3 + DSB)). SBP variability (SBPV), DBP variability (DBPV) and MAP variability (MAPV). EIV and EDV: cutaneous microcirculatory responses at the forearm by laser Doppler (DRT4, MOOR). Flow, speed and concentration were evaluated. Peak-Flow was considered normal >67% (group A) and abnormal <67% (group B). Rising and recovering time were measured too. An endothelium-independent response was evaluated by sodium nitroprusside iontophoresis. Large (LAEI) and small (SAEI) artery elasticity index and stroke volume (SV) by HDI/PulseWave CR-2000. Statistical analysis: Kolmogorov-Smirnov normality test, t-student, Pearson chi-square and linear regression, Mann-Whitney U. 1. The prevalence of abnormal EDV was N=27 (22,3 %).2. There was a significant correlation with age (r=0,284, p=0,002) and waist: p=0,029. 2-. Group B patients presented higher values in IR (p=0,034), CPRhs (p=0,011) and COMP (p= 0,004).3- The significant differences for the ABPM (Group B vs A) were: 24h-DBPV (p=0,015) and 24h-MAPV (p=0,043). 8. The significant differences for the CV Profiling System (Group B vs A) were: SAEI (p=0,005), and SV (p=0,010). 1.The prevalence of ED in the microcirculation was 22,3%. 2.There was a statistically significant correlation with age, CRPhs and IR 2-The correlation with COMP suggests an activation of the extracellular matrix.3-There was a statistically significant in correlation with DBP variability, heart rate, small artery elasticity index and stroke volume.

Automated electrochemical CV profiling of LED structures on wafer scale

A newly developed equipment is presented to perform (photo-)electrochemical (PEC) CV profiling in semiconductor structures. The equipment is fully automated to handle sample sizes from some mm2 up to 6″ wafers. Fully automated loading of the electrochemical cell, fluid handling system, automatic unloading of the fluid, and drying of the sample at the end of the measurement are incorporated into the setup. Furthermore, together with a wafer stepper it is possible to perform wafer topography measurements. The hardware makes use of a recently, especially for group III-nitrides developed etch procedure named “cyclic oxidation”: featuring high etch rates in the range of 3 μm/h for n- and p-type (Al,In)GaN layers together with mirror-like etched surface morphology. Using this new equipment, LED structures have been characterized by CV profiling. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Ultra-shallow arsenic implant depth profiling using low-energy nitrogen beams

Sputtering of silicon by low-energy nitrogen primary ion beams has been studied by a number of authors to characterize the altered layer, ripple formation and the sputtered yields of secondary ions [Surf. Sci. 424 (1999) 299; Appl. Phys. A: Mater. Sci. Process 53 (1991) 179; Appl. Phys. Lett. 73 (1998) 1287]. This study examines the application of low-energy nitrogen primary ion beams for the possible depth profiling of ultra-shallow arsenic implants into silicon. The emphasis of this work is on the matrix silicon signals in the pre-equilibrium surface region that are used for dose calibration. Problems with these aspects of the concentration depth profiling can give significant inconsistencies well outside the error limits of the quoted dose for the arsenic implantation as independently verified by CV profiling. This occurs during depth profiling with either oxygen primary ion beams (with and without oxygen leaks) or cesium primary ion beams.

SPV Monitoring of Near Surface Doping – Role of Boron-Hydrogen Interaction; Boron Passivation and Reactivation

ABSTRACTHydrogen is known to cause the passivation of boron acceptors after such processing steps as wet etching, reactive ion etching, sputter deposition of metal contacts, and Ar ion beam etching. Previous studies of this effect employed CV profiling, spreading resistance profiling, and SIMS measurements on samples diffused with deuterium. These methods are either destructive to the Si surface or require deposition of metal contact. In the present study we used a non-contact small signal ac-surface photovoltage technique, currentlyavailable in commercial diagnostic tools. Simultaneous measurements of the semiconductor surface barrier, Vsb, and the capacitance of the surface depletion layer, CD, give the concentration of boron acceptors in a submicron distance from the Si surface or Si/SiO2 interface. The technique has proven very successful in monitoring low dose implants and also near surface doping in oxidized wafers. Inbare silicon wafers the method occasionally indicated surface boron concentration noticeably below the bulk value. We found such behavior in wafers after the chemical cleaning, used to prepare a hydrogen terminated surface. Thermal annealing at temperatures from 150°C to 200°C reactivates the boron dopant. We will discuss the effect of various cleaning and annealing conditions on passivation and reactivation of boron acceptors in the near surface region. The results obtained with the non-contact SPV technique show excellent agreement with previous studies. They also provide a basis for reliable measurement of the boron concentration free of interference from hydrogen passivation.

Method to determine forward gate capacitance ofHFETs using resonance effect

A new method to determine gate capacitance under forward bias is presented. The method uses the frequency domain resonance of the real part of the Z11 parameter at microwave frequencies. This method extends the range of conventional CV profiling to higher forward gate bias regions. The result of this method helps to resolve the ambiguity of forward bias gate capacitance in large signal device models.

Structural and electrical properties of ZnSe laser diodes optimized by transmission electron microscopy, reflection high energy electron diffraction, X-ray diffraction and C-V profiling

The properties of ZnSe and ZnS x Se 1− x epilayers grown by molecular beam epitaxy deposited either directly on GaAs substrates or on GaAs buffer layers are compared with each other. The superior structural quality of the latter one is confirmed by reflection high energy electron diffraction (RHEED), X-ray diffraction (XRD) and transmission electron microscopy (TEM). Under optimized conditions nearly lattice matched ZnS x Se 1− x epilayers with full width at half maximum (FWHM) values down to 23 arc sec were achieved. The dependence on the type of dopant of the dislocation density and the depth of penetration related to the GaAs/ZnSe interface is discussed by cross-sectional TEM images. At the GaAs:Si/ZnSe:Cl interface a high-impedance layer was found and investigated by C−V profiling (CVP) and Van der Pauw (VdP) measurements for different initial growth conditions and for various ZnSe carrier concentrations. In addition the dislocations at the ZnSe/ZnS x Se 1− x interfaces were studied by TEM. Finally, we were able to improve the structural quality of the active area of blue green laser diodes by a special design of layer thicknesses.

Blue stimulated emission from a ZnSe p-n diode at low temperature

Laser diode structures have been fabricated using molecular beam epitaxy with iodine from an electrochemical source for the n-type doping and nitrogen from a plasma source for the p-type doping. CV profiling using electrochemical etching shows uniform p doping of 4×1017 cm−3 and n doping of 1×1018 cm−3. Under pulsed current excitation blue emission at 470 nm is observed at room temperature which increases in intensity at liquid helium temperatures. Above a current density threshold of 50 A cm−2 stimulated emission is observed between 448–473 nm with a complicated mode structure.

N-type doping of molecular beam epitaxial zinc selenide using an electrochemical iodine cell

The authors report the use of an electrochemical iodine cell to dope epitaxial ZnSe grown by molecular beam epitaxy over a range of carrier concentrations from 1016 to 1019 cm-3. The doping levels throughout the layers have been measured by electrochemical CV profiling and staircase doping structures have been used to calibrate the doping level in terms of the cell flux. Photoluminescence and Hall data confirm the growth of well-behaved n-type ZnSe.

Electrical characterization of iodine doped molecular beam epitaxial ZnSe

We report the use of an electrochemical iodine cell to dope epitaxial ZnSe grown by molecular beam epitaxy (MBE) over a range of carrier concentrations from 10 16 to 10 19 cm -3. The doping levels throughout the layers have been measured by electrochemical CV profiling and calibrated in terms of the cell flux. Photoluminescence and Hall data confirm the growth of well behaved n-type ZnSe.

Hydrogen Passivation and Reactivation of Bistable Thermal Donors in Silicon

ABSTRACTThe dissociation of Thermal Donor-hydrogen complexes is studied by infra-red absorption, CV and DLTS profiling. Silicon samples are prepared to contain only TD1 and TD2 and in particular only TD1 is exhibiting bistable properties. After hydrogen passivation, annealing in the dark under reverse bias leads to a first order reactivation of TD1 and TD2. A marked difference in the dissociation energies is found (ED(TD1 - H) = 1.67eV, ED (TD2 - H)≈ 1.9eV). Our results suggest that TD1 and TD2 have a different microscopic structure.

A new approach to CV profiling with sub-Debye-length resolution

A new method of doping profile determination from MOS deep-depletion capacitance-voltage characteristics is presented. It uses parameter optimization techniques and numerical solutions of Poisson's equation. Using this technique doping profiles which vary significantly over Debye length can be extracted accurately right up to the semiconductor surface. This makes the method very attractive for characterization of modern VLSI devices with rapidly varying doping profiles.

Schottky - Barrier Tunnelling Spectroscopy of Si:B Delta Layers

Delta doping in MBE has attracted considerable attention since its inception in 1980 [1], as a vehicle for studies of 2D phenomena and for its potential applications in, for example, FET devices [2] and I.R. detectors [3]. Boron delta doping in silicon is a recent development [4]. In previous papers we have reported on the growth, TEM, CV profiling, SIMS profiling and XRD characterisation of B delta layers [4,5,6]. It is of interest to know if the present growth method [4] produces a dopant sheet a monolayer wide or, in any event, what is the true width. Previous techniques [4,5,6] have yielded values between 0.4nm and 3nm for the width. Schottky barrier tunnelling spectroscopy provides further information on this question, but is also of interest for a study of the electronic structure of the delta layer. It has been used previously for a study of delta doping in III-V materials [7] and also for Sb delta doping in Si [8,9], but there have so far been no reports of its application to Si:B delta layers.

Band offset in GaAlAs and InGaAs: InP heterojunctions by electrochemical CV profiling

We report electrochemical CV measurement determination of the conduction band offset ΔEc of Ga 1−xAl xAs:Ga 1−yAl yAs heterojunctions (HJs) with x=0−0.21 and y≈0.4, as well as of In 0.53Ga 0.47As: InP HJs. The samples were grown by liquid phase epitaxy. We have obtained band offset ratios ΔEc/ΔEg≈0.6 and ΔEc/ΔEg≈0.36, respectively, for GaAlAs and InGaAs: InP HJs, where ΔEg is the HJ band gap energy difference. These results are consistent with recent data obtained by other techniques on similar HJs. In addition, the density of fixed interface charges are estimated and are apparently related to the doping of the large band gap layer of the HJ.

CV profiling on p-p- and n-s.i.-In 0.53Ga 0.47As/InP heterointerfaces

Our investigations on LPE grown p-p- and n-s.i.-In 0.53Ga 0.47As/InP heterointerfaces by means of CV profiling and magnetoresistivity measurements are presented. Measurements on p-p-heterojunctions indicate a valence band offset of Δ E v = 0 eV. Measurements on n-s.i.-het-erojunctions were analysed by Rhoderick's method. The results show a large scatter in interface properties across a wafer. CV profiles indicate an electron accumulation layer at the n-s.i.-InGaAs/InP interface which develops into a two-dimensional electron gas at lower temperatures (Shubnikov-de Haas oscillations).

Crystal Damage during CV Profiling

After CV measurements of and highly doped Si, using mercury as a Schottky contact, crystal damage on the diode electrode sometimes occurs as can be made visible by selective etching techniques. The presence of this damage appears to be related to the magnitude of the applied bias voltage and to a slight contamination of the mercury with dust particles. The penetration depth has been observed to be in the order of a few hundred nanometers.

Limitations of the CV technique for ion-implanted profiles

The CV profiling technique is reviewed and its validity and limitations are investigated, with special attention given to the case where the method is extended to the study of ion-implanted impurity distributions. A theoretical analysis is described which yields information about the dependence of CV measurements on impurity profile. The inverse problem is then considered and the results demonstrate that the depletion approximation formulas commonly used for the reduction of CV data to give doping profiles are misleading when applied to substrates with rapidly varying profiles as are generally the case for ion-implanted substrates. Examples of the profiles obtained for various shaped impurity distributions are given.