Passivation Of Acceptors Research Articles

Damage in III/V semiconductors caused by hard- and soft-etching plasmas

Damage in III/V semiconductors caused by processing in high- and low-density plasmas is investigated employing material-specific analytical methods. To distinguish the various regimes of damage, four different ambients out of the palette of plasma constituents were chosen: as borderline cases, argon which is associated with hard etching causing crystal lattice disordering until complete amorphization, and hydrogen which is the prototype of soft etching causing bond breaking between the lattice constituents without changing the crystal site, and the two model ambients Ar/Cl2 and Ar/CH4/Cl2/H2 which are widely used to etch Ga-containing compound semiconductors. Several probes and methods are employed which are selectively sensitive to the different kinds of damage: damage of the crystal lattice with photoluminescence, scanning electron microscopy and scanning transmission electron microscopy, and the concentration gradient of a chemically reactive species (hydrogen) with secondary ion mass spectrometry. Its reaction with lattice atoms (acceptor passivation), is recorded by capacitance/voltage and Hall measurements. For irreversible damage (knock out of atomic lattice sites), there can be detected only one damage zone reaching not deeper than 30 nm. The depth is inversely proportional to the lattice energy and proportional to the kinetic energy of the projectiles. In contrast to this rather shallow damage, the penetration depth of hydrogen amounts up to several microns. Since the subsequent passivation of acceptor atoms is a chemical reaction, it can be reverted at elevated temperatures. It has turned out, with all methods applied, that the gentlest ambient to etch Ga-containing III/V semiconductors is Ar/Cl2. This is not restricted to the smoothness of the surfaces but refers to all quantitative measurements which are applied in this study.

Hydrogen-acceptor interactions in diamond

Abstract Hydrogen-acceptor interactions are investigated in boron-doped diamond through deuterium diffusion experiments followed by SIMS measurements and through infrared absorption spectroscopy. From deuterium diffusion, we show that BD interactions can be properly demonstrated in low compensation B-doped homoepitaxial layers. However, the presence of defects in such layers strongly affects this interaction. The degree of passivation of boron acceptors by deuterium depends on the diffusion temperature. At 550°C or below, the B and D concentrations exactly match giving rise to a complete disappearance of the absorption bands related to the electronic transitions of neutral boron acceptors. Under thermal annealing above 500°C, (B,D) pairs dissociate and neutral boron acceptors recover. At deuterium diffusion temperatures of 700°C, the B passivation is absent.

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.

Capacitance–voltage profiling of deuterium passivation and diffusion in diamond Schottky diodes

Abstract Capacitance–voltage measurements have been performed on deuterated boron-doped natural type IIb diamond. They demonstrate the electrical passivation of the boron acceptors, which was manifested by a persistent decrease in capacitance after deuteration. Bias annealing experiments have been carried out to determine the charge state of the diffusing deuterium. The differences between annealing with or without bias lead to the conclusion that boron–deuterium complexes dissociate at about 750 K and that the released deuterium is positively charged.

Passivation of boron in diamond by deuterium

Capacitance–voltage measurements have been performed on deuterated boron-doped synthetic-type IIb diamond. They demonstrate the electrical passivation of the boron acceptors, which was manifested by a persistent decrease in capacitance after deuteration. The capacitance–voltage dependence is explained by means of a two-layer depletion width model.

Low temperature photoluminescence properties of p- and n-type Al x Ga 1- x As with x>0.42

The photoluminescence (PL) spectra of n- and p-type Al x Ga1−x As (x>0.42) grown by metalorganic vapor phase epitaxy (MOVPE) and liquid phase epitaxy show typically a broad PL band (BB) centered about 300meV below the near band-gap PL lines. In the MOVPE grown samples the BB is composed out of four lines. The BB intensity increases with the doping level and dominates the spectrum at concentrations > 1017 cm−3. The temperature dependence of the BB intensity shows two distinct maxima at ≈ 19K and ≈ 80K. Hydrogenation of MOVPE grown samples at 170°C reveal an effective passivation of the shallow acceptors and the centers associated with the BB line. On the contrary hydrogenation at temperatures >250°C leads to an increase in the BB intensity which is related with the evaporation of As from the surface and the generation of VAs in the layers at these temperatures. Our results suggest that the BB is related with isoelectronic centers formed when VAs and CAs or SiAs associate to form next nearest neighbor ion pairs. The PL is then due to a recombination of excitons in analogy to the case of (Zn, O) isoelectronic complexes in GaP.

Effects of hydrogen implantation into GaN

Proton implantation in GaN is found to reduce the free carrier density through two mechanisms – first, by creating electron and hole traps at around E C − 0.8 eV and E V + 0.9 eV that lead to compensation in both n- and p-type material, and second, by leading to formation of (AH)° complexes, where A is any acceptor (Mg, Ca, Zn, Be, Cd). The former mechanism is useful in creating high resistivity regions for device isolation, whereas the latter produces unintentional acceptor passivation that is detrimental to device performance. The strong affinity of hydrogen for acceptors leads to markedly different redistribution behavior for implanted H + in n- and p-GaN due to the chemical reaction to form neutral complexes in the latter. The acceptors may be reactivated by simple annealing at ⩾600°C, or by electron injection at 25–150°C that produces debonding of the (AH)° centers. Implanted hydrogen is also strongly attracted to regions of strain in heterostructure samples during annealing, leading to pile-up at epi–epi and epi–substrate interfaces. IR spectroscopy shows that implanted hydrogen also decorates V Ga defects in undoped and n-GaN.

Atomic hydrogen cleaning of polar III–V semiconductor surfaces

Atomic hydrogen (H*) generated by a simple thermal cracker source has been used to efficiently clean the polar surfaces of several III–V semiconductors at temperatures significantly lower than those normally required for oxide desorption. The process of atomic hydrogen cleaning (AHC) is demonstrated for the preparation of the (001) and (111)A surfaces of InAs, and the InSb(001) and GaSb(001) surfaces. Both the substrate anneal temperature and the required H* dose vary for the different materials, but in all cases clean, well-ordered surfaces can be produced, as determined by low energy electron diffraction (LEED) and Auger electron spectroscopy (AES). It is found that both the InAs and GaSb surfaces can be cleaned with H* exposures at a specific temperature (as low as 470 K for GaSb and 700 K for InAs); however, for InSb it is also necessary to supply an Sb 4 flux from a Knudsen cell to avoid decomposition of the surface. High resolution electron energy loss spectroscopy (HREELS) has been used to monitor the surface plasmon excitations in these doped materials to measure the carrier concentration in the near-surface region. It is found that no measurable passivation of donors or acceptors occurs in either the n-type or p-type materials studied. In addition, and in contrast to ion sputtering procedures, no defect induced increase in the carrier concentration occurs as a result of atomic hydrogen cleaning.

Performance and Stability of MOVPE-Grown Carbon-Doped InP/InGaAs HBT's Dehydrogenated by an Anneal after Emitter Mesa Formation

A high-temperature anneal of 500°C for 5 min after emitter mesa formation is effective in completely reversing the hydrogen passivation of carbon acceptors in InP/InGaAs heterostructure bipolar transistors. Fabricated devices show a base hole concentration as high as 5 ×1019 cm-3 and a maximum oscillation frequency above 200 GHz. However, this technique simultaneously causes damage to the emitter mesa surface and degrades current gain. In order to avoid such undesirable effects, one has to carefully optimize the anneal conditions and/or select the optimum crystallographic orientation of the emitter mesa so as to increase the thermal stability of InP sidewalls. Preliminary bias-temperature stress tests were also performed to examine the stability of base-emitter junctions. The results show that the stability strongly depends on the emitter mesa orientation. Promising results are obtained from devices whose emitter orientation is parallel to the Primary Flat of (100)-oriented InP substrates.

Hydrogen in GaN-Experiments

ABSTRACTHydrogen is an important component of the gas phase growth chemistry for GaN (eg. NH3, (CH 3)3 Ga)and the processing environment for subsequent device fabrication (eg. SiH4 for dielectric deposition, NH3 or H2 annealing ambients), and is found to readily permeate into heteroepitaxial material at temperatures ≤200°C. Its main effect has been the passivation of Mg acceptors in p-GaN through formation of neutral Mg-H complexes, which can be dissociated through minority-carrier (electron) injection or simple thermal annealing. Atomic hydrogen is also found to passivate a variety of other species in GaN, as detected by a change in the electrical or optical properties of the material. An example is the increase in luminescence efficiency of Er3+ ions in AIN after hydrogenation, through passivation of non-radiative states that would be an alternative path for de-excitation. The injection of hydrogen during a large variety of device fabrication steps has been detected by SIMS profiling using 2H isotopic labeling. Basically all of the acceptor species in GaN, namely Mg, C, Ca and Cd are found to form complexes with hydrogen.

A study of electrically active defects created in p-InP by CH4:H2 reactive ion etching

The electrical effects of reactive ion etching (RIE) of p-InP by CH4:H2 are investigated. By using optical deep-level transient spectroscopy, several deep-level defects could be detected. The main defect (E3) is found to be a donor with an energy level at Ec−0.38 eV. From depth profiles of both the net acceptor concentration and this defect, it follows that after RIE, the E3 defects are passivated by hydrogen. Simultaneous passivation of both acceptors and donors on p-InP is reported. Subsequent rapid thermal annealing at increasing temperatures shows that the E3 defects are first depassivated and then annealed out. The change of the Schottky barrier height with the anneal temperature could be explained by Fermi-level pinning due to E3 and depinning either by its passivation for low enough temperatures or by its annealing out at higher temperatures. Some possibilities concerning the physical nature of E3 are discussed.

Interface formation between hydrogen terminated Si(111) and amorphous hydrogenated carbon (a-C:H)

In the last few years heterostructures consisting of a-C:H on top of crystalline silicon have revealed a number of interesting properties for electronic applications, for example, as a photodiode (see Ref. 1) or, very recently, as cold cathode electron emitter (see Ref. 2). For those applications the interface properties of the heterostructure play a key role. In this article the electronic and chemical nature of the interface between plasma deposited a-C:H in the form of diamondlike carbon (DLC) and hydrogen terminated silicon (111) was determined by in situ core level and valence band photoemission spectroscopy. The quantitative analysis of core level shifts and intensities indicate that both, an interface layer of mixed composition and a pure a-C:H layer, grow simultaneously with relative growth rates of 2:1 during the initial stages of the interface formation. The interface layer is first carbon rich and then approaches stoichiometric composition which is reached at an interface thickness of 18 Å. Then a reactive SiC interface is completed and acts as a diffusion barrier which prevents further extension of the interface region when the deposition of a-C:H proceeds. Aside from an acceptor passivation of the Si substrate, due to H atoms from the plasma, no overlayer induced band bending is measured. The valence band offset between Si and DLC is determined as 0.7±0.1 eV with the valence band edge of DLC below that of silicon.

Hydrogen in carbon-doped GaAs base layer of GaInP/GaAs heterojunction bipolar transistors

Hydrogen incorporation into heavily carbon-doped GaAs grown by metal-organic vapour phase epitaxy using carbon tetrabromide (CBr 4) has been studied. In the base layer of as-grown GaInP/GaAs heterojunction bipolar transistors (HBTs), about 20% of the carbon acceptors are found to be passivated by hydrogen. The outdiffusion of this hydrogen during an ex situ annealing at 450 °C in nitrogen, which is effective for carbon-doped single layers, is blocked by n-type capping layers in HBTs. An in situ annealing step was found to be suitable to reduce the acceptor passivation in HBTs to about 10%.

MOVPE growth of hetero-bipolar-transistors using CBr4 as carbon dopant source

Carbon doping of GaAs with carbon tetrabromide (CBr 4 ) in low pressure MOVPE has been investigated and applied to the fabrication of GaInP/GaAs HBTs. Especially the hydrogen incorporation and the associated acceptor passivation has been studied. The hydrogen found in single GaAs:C layers is predominantly incorporated during cooling the sample under AsH 3 after growth. n-Type capping layers can block this H indiffusion and GaAs:C base layers in HBTs show much lower H concentrations than GaAs:C single layers without a cap. A further reduction of acceptor passivation is possible by optimization of the growth procedure. First HBTs processed from layers with a base that was doped using CBr 4 show promising DC and HF performance (β = 45, f T = 26 GHz for 2 X 20 μm 2 devices).

More progressive technology of GaSb single crystal growth

GaSb single crystals were grown by the Czochralski method without encapsulant in an atmosphere of ionized hydrogen. It has been found that the resistivity increased by more than one order of magnitude (0.8–1.0Ω cm) and free carrier concentration decreased to the value of (1–2) × 1016 cm−3 in comparison with the crystals grown under molecular hydrogen atmosphere. A certain asymmetry in acceptor and donor passivation is assumed because the Hall concentration does not vary along the direction of crystal growth. Donors are passivated more than acceptors, which should be confirmed by increasing resistivity and decreasing mobility.

The role of hydrogen in low-temperature MOVPE growth and carbon doping of In0.53Ga0.47As for InP-based HBT

Hydrogen radicals are decisive for the low-temperature growth and carbon doping of In0.53Ga0.47As in LP-MOVPE. This is demonstrated for the growth of highly p-type doped In0.53Ga0.47As layers with CCl4 as dopant source. Perturbed angular correlation measurements (PAC) were used to investigate the passivation of acceptors by hydrogen in low-temperature grown In0.53Ga0.47As. Based on the above analysis an InP-based layer stack is developed which employs low-temperature growth of the base layer, high-temperature growth of the remaining HBT layers, and an in situ post-growth annealing under TMAsN2 ambient.

Atomic structure of defect complexes containing carbon and hydrogen in GaAs.

We study the hydrogen passivation of carbon acceptors and the stability of defect complexes containing carbon and hydrogen in GaAs through first-principles pseudopotential calculations. A carbon-hydrogen ${\mathrm{C}}_{\mathrm{As}}^{\mathrm{\ensuremath{-}}}$-(${\mathrm{HC}}_{\mathrm{As}}$${)}^{0}$ complex with two ${\mathrm{C}}_{\mathrm{As}}$ atoms at second-neighbor As sites is found to be energetically more favorable than the isolated configuration of ${\mathrm{C}}_{\mathrm{As}}^{\mathrm{\ensuremath{-}}}$ and H-${\mathrm{C}}_{\mathrm{As}}$. We also find that a (H-${\mathrm{C}}_{\mathrm{As}}$${)}_{2}$ complex containing two H atoms is more stable than two isolated H-${\mathrm{C}}_{\mathrm{As}}$ pairs. Hydrogen dissociation from the ${\mathrm{C}}_{\mathrm{As}}^{\mathrm{\ensuremath{-}}}$-(${\mathrm{HC}}_{\mathrm{As}}$${)}^{0}$ center upon annealing leads to the formation of a ${\mathrm{C}}_{\mathrm{As}}$-${\mathrm{C}}_{\mathrm{As}}$ pair, and the ${\mathrm{C}}_{\mathrm{As}}$-${\mathrm{C}}_{\mathrm{As}}$ complex subsequently dissociates into two isolated ${\mathrm{C}}_{\mathrm{As}}$ acceptors. Here we propose a dissociation process that involves a C-C split-interstitial complex at an As site and a second-neighbor As vacancy, with an energy barrier of about 1.7 eV, which is similar to that for Zn diffusion. \textcopyright{} 1996 The American Physical Society.

Effect of extended defects on the formation and dissociation kinetics of Zn–H complexes in heteroepitaxial p-type InP layers

Hydrogen passivation of Zn acceptors and Zn–H dissociation kinetics are compared for homoepitaxial and lattice-mismatched heteroepitaxial n+p InP structures. Doping profile measurements show a pronounced increase in the depth and degree of passivation in the p-type region of the heteroepitaxial samples indicating enhanced diffusion of hydrogen along dislocations, followed by additional Zn deactivation. Moreover, the strong affinity between hydrogen and extended defects is found to aid the subsequent dissociation of the Zn–H complexes as indicated by (i) reverse bias annealing (RBA) studies which show that the Zn–H dissociation energy decreases from 1.19 eV in homoepitaxial samples to 1.12 eV in heteroepitaxial samples, and (ii) enhanced passivation of extended defect-related traps by hydrogen that is liberated from Zn acceptors during the RBA process as determined by deep level transient spectroscopy.

Hydrogenation passivation of acceptors in MOCVD grown p-INSB

We report on the effects of hydrogenation of InSb GaAs epilayers. The as-grown MOCVD InSb is p-type with an acceptor activation energy of 16 meV. The 16 meV impurity, however, is fully passivated during protonation in a hydrogen microwave plasma, revealing a shallower, 2 meV acceptor which appears unaffected by further processing. The material remains p-type after hydrogenation and the Fermi level calculations reveal that the majority carriers over the entire temperature range are holes. The electron to hole mobility ratio is sufficiently large however, that the Hall data shows evidence for an apparent type conversion.

Hydrogen passivation of Ca acceptors in GaN

Exposure to a hydrogen plasma at 250 °C of p-type GaN (Ca) prepared by either Ca+ or Ca+ plus P+ co-implantation leads to a reduction in sheet carrier density of approximately an order of magnitude (1.6×1012 cm−2 to 1.8×1011 cm−2), and an accompanying increase in hole mobility (6 cm2/V s to 18 cm2/V s). The passivation process can be reversed by posthydrogenation annealing at 400–500 °C under a N2 ambient. This reactivation of the acceptors is characteristic of the formation of neutral (Ca–H) complexes in the GaN. The thermal stability of the passivation is similar to that of Mg–H complexes in material prepared in the same manner (implantation) with similar initial doping levels. Hydrogen passivation of acceptor dopants in GaN appears to be a ubiquitous phenomenon, as it is in other p-type semiconductors.