The defect density of a SiNx/In0.53Ga0.47As interface passivated using (NH4)2Sx

Passivation of the electronic defect states at a SiN_x/InGaAs interface has been achieved using (NH₄)₂S_x treatments of the InGaAs surface. The X-ray photoelectron spectroscopy technique was used to investigate the mechanism of sulfur passivation. The results indicate that sulfur treatment can effectively erase the native oxides, and S-In, S-Ga and S-As bondings are formed after sulfidation. The fabrication of Au/SiN_x/InGaAs metal–insulator–semiconductor diodes has been achieved by depositing a layer of SiN_x on (NH₄)₂S_x-treated n-InGaAs using the plasma enhanced chemical vapor deposition technique. The effect of passivation on the InGaAs surface before and after annealing was evaluated by current–voltage and capacitance–voltage measurements. The results indicate that the SiN_x passivation layer exhibits good insulative properties. The annealing contributes to the decrease of the fixed charge density and the minimum surface state density, which are 4.5×10¹¹ cm^-2 and 3.92×10¹¹ cm^-2 eV^-1, respectively. A 256×1 InP/InGaAs/InP heterojunction short-wavelength infrared detector, fabricated with the sulfidation plus a SiN_x passivation layer, has shown a good response uniformity of 4.81%. PACS 73.20.At; 73.40.Kp; 73.40.Rw; 81.40.Rs; 71.55.Eq     

Surface passivation of In0.83Ga0.17As photodiode with high-quality SiN layer fabricated by ICPCVD at the lower temperature

The surface passivation of low-temperature-deposited SiN_x films has been investigated in PIN type In_0.83Ga_0.17As photodiodes. In contrast to SiN_x films (330 °C) fabricated by PECVD (Plasma enhanced chemical vapor deposition), the low-temperature-deposited SiN_x films (75 °C) fabricated by ICPCVD (Inductively coupled plasma chemical vapor depositon) have a good effect on passivation of In_0.83Ga_0.17As photodiodes, which caused reductions of dark current as large as 2–3 orders of magnitude at the same test temperature 200 K. The effects of low-temperature-deposited SiN_x passivations with lowrate (∼16 nm/min) model were compared to the ones with highrate (∼100 nm/min) model. SiN_x films with lowrate model have a better effect on reducing dark current of the photodiodes. The different SiN_x films were studied by SIMS. The results show that the content of oxides in SiN_x layer fabricated by PECVD is 2 orders of magnitude more than that in SiN_x layer fabricated by ICPCVD which could be the reason that low-temperature-deposited SiN_x passivation leads to higher performance. Further, the dark current density of the photodiodes with lowrate-deposited SiN_x passivations does not show the dependence on the perimeter-to-area(P/A) of the junction.     

Electric-stress reliability and current collapse of different thickness SiNx passivated AlGaN/GaN high electron mobility transistors

This paper investigates the impact of electrical degradation and current collapse on different thickness SiNx passivated AlGaN/GaN high electron mobility transistors.It finds that higher thickness SiNx passivation can significantly improve the high-electric-field reliability of a device.The degradation mechanism of the SiNx passivation layer under ON-state stress has also been discussed in detail.Under the ON-state stress,the strong electric-field led to degradation of SiNx passivation located in the gate-drain region.As the thickness of SiNx passivation increases,the density of the surface state will be increased to some extent.Meanwhile,it is found that the high NH 3 flow in the plasma enhanced chemical vapour deposition process could reduce the surface state and suppress the current collapse.     

Effects of the passivation of SiNx with various growth stoichiometry on the high temperature transport properties of the two-dimensional electron gas in AlxGa1−xN/GaN heterostructures

Effects of the passivation of SiN_x on the high temperature transport characteristics of the two-dimensional electron gas (2DEG) in unintentionally doped Al_xGa_1−xN/GaN heterostructures have been investigated by means of high temperature Hall measurements. The 2DEG density increases much after SiN_x passivation, and the increment is proportional to the Si content in SiN_x layer, indicating that the increment is mainly caused by ionized Si atoms at the SiN/Al_xGa_1−xN interface with dangling bonds or by Si atoms incorporated into the Al_xGa_1−xN layer during the SiN_x growth, which is approved by strain analysis and X-ray photoemission spectroscopy (XPS). There is lower 2DEG mobility at room temperature in a passivated sample than in an unpassivated one. However, the 2DEG mobility becomes to be higher in a passivated sample than in an unpassivated one when the temperature is above 250 °C, which is suggested to be caused by different subband occupation ratios in the triangular quantum well at the heterointerface before and after passivation.     

Study of the multiple-negative-differential-resistance (MNDR) switching behaviors based on heterojunction bipolar transistor (HBT) structures

In this paper, we demonstrate multiple-negative-differential-resistance (MNDR) switching behaviors based on the InGaP/GaAs heterostructure-emitter bipolar transistor (HEBT) and InGaAlAs/InP heterojunction bipolar transistor (HBT) structures. The devices act like conventional HBTs under forward operation mode. The proposed HEBTs show lower offset voltage due to the correct design of the emitter thickness. On the other hand, MNDR phenomena resulting from avalanche multiplication, confinement effects and the potential redistribution process are observed under inverted operation mode for both devices. In addition, three-terminal NDR characteristics are investigated under the applied base currentI_B . Moreover, for the InGaAlAs/InP HBT, anomalous multiple-route and multiple-step current–voltage (I–V) characteristics at 77 K are observed due to the insertion of a InGaAs quantum well (QW) between the base and collector layers.     

Influence of SiNx:H film properties according to gas mixture ratios for crystalline silicon solar cells

The Hydrogenated silicon nitride (SiN_x:H) using plasma enhanced chemical vapor deposition is widely used in photovoltaic industry as an antireflection coating and passivation layer. In the high temperature firing process, the SiN_x:H film should not change the properties for its use as high quality surface layer in crystalline silicon solar cells. For optimizing surface layer in crystalline silicon solar cells, by varying gas mixture ratios (SiH₄ + NH₃ + N₂, SiH₄ + NH₃, SiH₄ + N₂), the hydrogenated silicon nitride films were analyzed for its antireflection and surface passivation (electrical and chemical) properties. The film deposited with the gas mixture of SiH₄ + NH₃ + N₂ showed the best properties in before and after firing process conditions.The single crystalline silicon solar cells fabricated according to optimized gas mixture condition (SiH₄ + NH₃ + N₂) on large area substrate of size 156 mm × 156 mm (Pseudo square) was found to have the conversion efficiency as high as 17.2%. The reason for the high efficiency using SiH₄ + NH₃ + N₂ is because of the good optical transmittance and passivation properties. Optimized hydrogenated silicon nitride surface layer and high efficiency crystalline silicon solar cells fabrication sequence has also been explained in this study.     

Characterization of SiON/InP MOS structure with sulfidation, fluorination, and hydrogenation

Liquid phase deposited SiON film on InP with (NH₄)₂S treatment shows superior electrical characteristics due to the reduction of native oxides and sulfur passivation. Simultaneously, HF in SiON liquid phase deposition solution can effectively reduce residual native oxides on InP and provide fluorine passivation in SiON/InP film and interface. With post-metallization annealing (PMA), hydrogen ions can further passivate defects in SiON/InP film and interface. With these treatments, the PMA-LPD-SiON/(NH₄)₂S-treated InP MOS structure shows excellent electrical characteristics. With the physical thickness of 5.4 nm, the leakage current densities can be as low as 1.25×10^?7 and 6.24×10^?7 A/cm² at ±2 V, and the interface state density is 3.25×10¹¹ cm^?2?eV^?1.     

Simulation study of InP-based PNP heterojunction bipolar transistors and incorporation of nonclassical effects

This paper describes a numerical approach to the modeling of PNP HBTs in the InP-based materials systems (InP/InGaAs and InAlAs/InGaAs). Initial device analysis was achieved in the drift-diffusion limit by self-consistent numerical solution of the Poisson, carrier continuity and conductor equations subject to the device's geometry and boundary conditions imposed by the device's biasing. Simulation results are compared with the available experimental results and good agreement is found. For the InP/InGaAs and InAlAs/InGaAs heterojunctions, the valence band discontinuities are larger than for the AlGaAs/GaAs system so grading of the emitter-base junction and tunneling effects are important. For completeness, nonclassical effects were also considered. For the emitter-base junctions, hole tunneling was considered, particularly at low forward bias. The inverse dependence of the hole tunneling on effective mass was found to lead to significantly more light hole than heavy hole tunneling in calculating the emitter injection current. In addition, since very narrow base regions (25-35 nm) can be employed while keeping the base spreading resistance low due to the electron's higher mobility, ballistic hole transport should also be considered.     

A hybrid model to calculate the forward delay time of heterojunction bipolar transistors

The forward delay time (τ_F) of heterojunction bipolar transistors (HBTs) is calculated using a hybrid model of carrier transport. A rigorous quantum-mechanical treatment of electron tunneling and thermionic emission across the spike at the emitter-base junction is used to determine the energy of the electron flux injected into the base region. This flux is used as an initial distribution in a regional Monte Carlo simulator to model electron transport from base to sub-collector. In this paper, we estimate the base transit time using the impulse response technique and the collector delay time using the expression of Laux and Lai (IEEE Electron Device Letters, 11, 174, 1990). Improvements to the hybrid model proposed here to reduce some of the discrepancies between measured and calculated values of ƒ_τ for some InAlAs/InGaAs and InP/InGaAs structures reported in the literature are discussed.     

Surface passivation of InGaP/GaAs HBT using silicon-nitride film deposited by ECR-CVD plasma

In this paper we have developed a passivation technique with silicon-nitride (SiN_X) film that requires no surface pre-treatment, and is fully compatible to monolithic microwave integrated circuits (MMICs). The nitride depositions were carried out by ECR-CVD (electron cyclotron resonance-chemical vapor deposition) directly over InGaP/GaAs heterojunction structures, which are used for heterojunction bipolar transistors (HBTs). Optical emission spectrometry (OES) was used for plasma characterization, and low formation of H and NH molecules in the gas phase was detected at pressure of 2.5 mTorr. These molecules can degrade III-V semiconductor surfaces due to the preferential loss of As or P and hydrogen incorporation at the substrate. The substrates were cleaned with organic solvents using a Sox-let distillate. The ECR depositions were carried out at a fixed substrate temperature of 20 °C, SiH₄/N₂ flow ratio of 1, Ar flow of 5 sccm pressure of 2.5 mTorr and microwave (2.45 GHz) power of 250 W and RF (13.56 MHz) power of 4 W. We have applied this film for InGaP/GaAs HBT fabrication process with excellent results, where two major contribuiton is related to this passivation technique, the enhancement in the transistor dc gain β and the improvement in the signal-to-noise ratio when compared unpassivated and passivated devices.     

Photoluminescence properties of SiNx/Si amorphous multilayer structures grown by plasma-enhanced chemical vapor deposition

Very thin (nanometric) silicon layers were grown in between silicon nitride barriers by SiH₂Cl₂/H₂/NH₃ plasma-enhanced chemical vapor deposition (PECVD). The multilayer structures were deposited onto fused silica and silicon substrates. Deposition conditions were selected to favor Si cluster formation of different sizes in between the barriers of silicon nitride. The samples were thermally treated in an inert atmosphere for 1 h at 500 °C for dehydrogenation. Room-temperature photoluminescence (RT-PL) and optical transmission in different ranges were used to evaluate the optical properties of the structures. UV-VIS absorption spectra present two band edges. These band edges are well fitted by the Tauc model typically used for amorphous materials. RT-PL spectra are characterized by strong broad bands, which have a blue shift as a function of the deposition time of the silicon layer, even for as-grown samples. The broad luminescence could be associated with the confinement effect in the silicon clusters. After annealing of the samples, the PL bands red shift. This is probably due to the thermal decomposition of N-H bonds with further effusion of hydrogen and better nitrogen passivation of the nc-Si/SiN_x interfaces.     

High-Breakdown-Voltage Submicron InGaAs/InP Double Heterojunction Bipolar Transistor with ft=170GHz and fmax=253GHz

The layer structure of InGaAs/InP double heterojunction bipolar transistor (DHBT) is designed to enhance the frequency performance and breakdown voltage. The composition-graded base structure is used to decrease the base transit time. The InGaAs setback layer and two highly doped InGaAsP layers are used to eliminate the conduction band spike of the collector. The submicron-emitter InGaAs/InP DHBT is fabricated successfully. The base contact resistance is greatly decreased by optimization of contact metals. The breakdown voltage is more than 6V. The current gain cutoff frequency is as high as 170GHz and the maximum oscillation frequency reached 253GHz. The DHBT with such high performances can be used to make W-band power amplifier.     

Changes in optical and electrical properties and surface recombination velocity of n-type GaN due to (NH4)2Sx treatment

We have employed the photoluminescence (PL), surface photovoltage spectroscopy (SPS) and Hall effect measurements to study the effects of (NH₄)₂S_x treatment on the optical and electrical properties of n-type GaN (n-GaN) in this study. (NH₄)₂S_x treatment of n-GaN led to the decrease of the surface recombination velocity and the increase of the band-edge emission intensity, due to the accumulation of majority carriers and the repulsion of minority carriers near the (NH₄)₂S_x-treated n-GaN surface, the removal of the native oxide existed on the n-GaN, and sulfur passivation.     

Interface property of silicon nitride films grown by inductively coupled plasma chemical vapor deposition and plasma enhanced chemical vapor deposition on In0.82Al0.18As

Au/silicon nitride/In_0.82Al_0.18As metal insulating semiconductor (MIS) capacitors were fabricated and then investigated by capacitance voltage (C–V) test at variable frequencies and temperatures. Two different technologies silicon nitride (SiN_x) films deposited by inductively coupled plasma chemical vapor deposition (“ICPCVD”) and plasma enhanced chemical vapor deposition (“PECVD”) were applied to the MIS capacitors. Fixed charges (N_f), fast (D_it) and slow (N_si) interface states were calculated and analyzed for the different films deposition MIS capacitors. The D_it was calculated to be 4.16 × 10¹³ cm⁻² eV⁻¹ for “ICPCVD” SiN_x MIS capacitors, which was almost the same to that of “PECVD” SiN_x MIS capacitors. The D_it value is obviously higher for the extended wavelength In_xGa_1−xAs (x > 0.53) epitaxial material as a result of lattice mismatch with substrate. Compared to the results of “PECVD” SiN_x MIS capacitors, the N_si was significantly lower and the N_f was slightly lower for “ICPCVD” SiN_x MIS capacitors. X-ray photoelectron spectroscopy (XPS) analysis shows good quality of the “ICPCVD” grown SiN_x. The low temperature deposited SiN_x films grown by “ICPCVD” show better effect on decreasing the dark current of In_xGa_1−xAs photodiodes.     

Effective surface passivation of crystalline silicon using ultrathin Al2O3 films and Al2O3/SiNx stacks

We measure surface recombination velocities (SRVs) below 10 cm/s on p‐type crystalline silicon wafers passivated by atomic–layer–deposited (ALD) aluminium oxide (Al₂O₃) films of thickness ≥10 nm. For films thinner than 10 nm the SRV increases with decreasing Al₂O₃ thickness. For ultrathin Al₂O₃ layers of 3.6 nm we still attain a SRV < 22 cm/s on 1.5 Ω cm p‐Si and an exceptionally low SRV of 1.8 cm/s on high‐resistivity (200 Ω cm) p‐Si. Ultrathin Al₂O₃ films are particularly relevant for the implementation into solar cells, as the deposition rate of the ALD process is extremely low compared to the frequently used plasma‐enhanced chemical vapour deposition of silicon nitride (SiN_x). Our experiments on silicon wafers passivated with stacks composed of ultrathin Al₂O₃ and SiN_x show that a substantially improved thermal stability during high‐temperature firing at 830 °C is obtained for the Al₂O₃/SiN_x stacks compared to the single‐layer Al₂O₃ passivation. Al₂O₃/SiN_x stacks are hence ideally suited for the implementation into industrial‐type silicon solar cells where the metal contacts are made by screen‐printing and high‐temperature firing of metal pastes. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

High-Speed InGaAs/InP Double Heterostructure Bipolar Transistor with High Breakdown Voltage

e design and fabricate an InGaAs/InP double heterostructure bipolar transistor (DHBT). The spike of the conduction band discontinuity between InGaAs base and InP collector is successfully eliminated by insertion of an InGaAs layer and two InGaAsP layers. The current gain cutoff frequency and maximum oscillation frequency are as high as 155 and 144GHz. The breakdown voltage in common-emitter configuration is more than 7V. The high cutoff frequency and high breakdown voltage make high-speed andhigh-power circuits possible     

Functional heterostructure-emitter bipolar transistor (HEBT) with graded-confinement and pseudomorphic-base structure

In this paper, a new functional heterostructure-emitter bipolar transistor (HEBT) with a graded Al_xGa_1 − xAs confinement layer and a pseudomorphic InGaAs/GaAs base structure is fabricated and demonstrated. Due to the insertion of an InGaAs quantum well (QW) between the emitter–base (E–B) junction, the valence band discontinuity can be enhanced and a high emitter injection efficiency may be achieved. Furthermore, the potential spike of the graded Al_xGa_1 − xAs/GaAs heterojunction is expected to be smoothed out which results in a lower offset voltage. The excellent transistor characteristics include a high current gain of 120 and a low offset voltage of 100 mV. In addition, an interesting S-shaped multiple negative differential resistance (MNDR) phenomenon is observed in the inverted operation mode. This may be attributed to an avalanche multiplication and a sequential two-stage barrier lowering effect resulting from the accumulation of holes at the base and electrons at the InGaAs QW, respectively. Consequently, owing to the remarkable transistor performance and MNDR characteristics, the studied HEBT shows good promise for applications in amplifiers and multiple-valued logic circuits.     

PASSIVATION OF THE InP(100) SURFACE USING (NH4)2Sx

InP(100) surface treated with (NH₄)₂S_x has been investigated by using photolumines-cence(PL), Auger electron spectroscopy and X-ray photoelectron spectroscopy, It is found that PL intensity increased by a factor of 3.3 after (NH₄)₂S_x passivation and the sulfur remained on the surface only bonded to indium, not to phosphorus. This suggests that the sulfur atoms replace the phosphorus atoms on the surface and occupy the phosphorus vacancies.     

Si-rich SiNx rear passivated c-Si solar cell with a novel antimony Local Back Surface Field formed by Laser Fired Contact

Local Back Contact (LBC) crystalline silicon solar cell with novel antimony (Sb) Local Back Surface Field (LBSF) are reported. The Sb LBSF is formed at low temperature with a Laser Fired Contacts (LFC) process. To improve the solar cell parameters of Sb LBSF, the rear passivation layer with SiN_x is optimized by varying the refractive index. The Si-rich SiN_x with a refractive index (n) of 2.7 possesses high lifetime of 2 ms with reduced absorption at a longer wavelength. The increase in lifetime is analyzed with Si–H bond concentration by FTIR. A 100 nm thick Sb layer with low laser power of 44 mW resulted in a junction depth of 500 nm with a carrier concentration of 5 × 10²⁰ cm^?3. The improved rear passivation with Si-rich SiN_x, the optimized Sb thickness yielded the best electrical results, with open circuit voltage (V_oc) of 643 mV and efficiency of 19.25%, compared to the reference cell with V_oc of 625 mV and efficiency of 18.20%.     

Growth and characterization of silicon nitride films on various underlying materials

Characteristics of silicon nitride (SiN_x:H) films, grown by plasma enhanced chemical vapor deposition (PECVD) on various metals such as Ta, IrMn, NiFe, Cu, and CoFe at various temperatures down to 100 °C, were studied using measurements of BHF etch rate, surface roughness and Auger electron spectroscopy (AES). The results were compared with those obtained for SiN_x:H films on Si. The deposition rate of SiN_x:H films increased slightly as deposition temperature decreased, and showed a weak dependence on the underlying materials. The surface of the nitride films deposited on all underlying materials at lower temperatures (below 150 °C) became rougher. In particular, a bubble-like surface was observed on the nitride film deposited on NiFe at 100 °C. At higher deposition temperatures (above 200 °C), SiN_x:H films on all the above metals had small RMS values, except for films on Cu which cracked at 250 °C. BHF (10:1) etch rate increased dramatically for nitride films deposited below 150 °C. For different underlying films, the BHF etch rate was quite different, but exhibited the same trend with decrease in deposition temperature. AES measurements showed that Si and N concentrations in the SiN_x:H films were only slightly different for the various deposition temperatures and underlying materials. AES depth profile of nitride films indicated that both surface O content and the depth of oxygen penetrating into SiN_x:H increased for low temperature-deposited films. However, there was no observed oxygen signal from within the films, even for films deposited at 100 °C, and both Si and N concentrations were uniform throughout the film. Received: 26 October 2001 / Accepted: 2 March 2001 / Published online: 20 June 2001