Photoluminescence Surface State Spectroscopy Research Articles

XPS, electric and photoluminescence-based analysis of the GaAs (1 0 0) nitridation

In this paper, nitridation process of GaAs (1 0 0) substrates was studied in-situ using X-ray photoelectron spectroscopy (XPS) and ex-situ by means of electrical method I– V and photoluminescence surface state spectroscopy (PLS 3) in order to determine chemical, electrical and electronic properties of the elaborated GaN/GaAs interfaces. The elaborated structures were characterised by I– V analysis. The saturation current I S, the ideality factor n, the barrier height Φ Bn and the serial resistance R S are determined. The elaborated GaN/GaAs structures are also exhibited a high PL intensity at room temperature. From the computer-aided analysis of the power-dependent PL efficiency measurements (PLS 3 technique), the value of the interface state density N SS( E) close to the mid-gap was estimated to be in the range of 2–4 × 10 11 eV −1 cm −2, indicating a good electronic quality of the obtained interfaces. Correlation among chemical, electronic and electrical properties of the GaN/GaAs interface was discussed.

Photoluminescence and capacitance–voltage characterization of GaAs surface passivated by an ultrathin GaN interface control layer

A novel surface passivation technique for GaAs using an ultrathin GaN interface control layer (GaN ICL) formed by surface nitridation was characterized by ultrahigh vacuum (UHV) photoluminescence (PL) and capacitance–voltage ( C– V) measurements. The PL quantum efficiency was dramatically enhanced after being passivated by the GaN ICL structure, reaching as high as 30 times of the initial clean GaAs surface. Further analysis of PL data was done by the PL surface state spectroscopy (PLS 3) simulation technique. PL and C– V results are in good agreement indicating that ultrathin GaN ICL reduces the gap states and unpins the Fermi level, realizing a wide movement of Fermi level within the midgap region and reduction of the effective surface recombination velocity by a factor of 1/60. GaN layer also introduced a large negative surface fixed charge of about 10 12 cm −2. A further improvement took place by depositing a Si 3N 4 layer on GaN ICL/GaAs structure.

Properties of Surface States on GaN and Related Compounds and Their Passivation by Dielectric Films

ABSTRACTThis paper reviews the authors′ recent efforts to clarify the properties of electronic states near surfaces of GaN and AlGaN by using variousin-situandex-situcharacterization techniques, including UHV contact-less C-V, photoluminescence surface state spectroscopy (PLS3), cathode luminescence in-depth spectroscopy (CLIS),and gateless FET techniques that have been developed by the authors’ group.As a result, a model including a U-shaped surface state continuum, having a particular charge neutrality level, combined with frequent appearance of near-surface N-vacancy related deep donor states having a discrete level at Ec - 0.37eV is proposed as a unified model that can explain large gate leakage currents and current collapse in AlGaN/GaN HFETs. Hydrogen plasma treatment and SiO2deposition increase N-vacancy related deep donors. Reasonably good surface passivation can be achieved by ECR-plasma SiNx films and by ECR-plasma oxidized Al2O3films both combined with ECR N2plasma treatment.

MBE growth and applications of silicon interface control layers

Fermi level pinning phenomenon at surfaces and interfaces of III–V materials is a still unsolved key issue and causes various unwanted problems in devices. In this paper, the present status of an approach to passivate surface states by an MBE-grown silicon interface control layer (Si ICL) is reviewed from both theoretical and experimental view points. First, UHV-based in situ surface characterization techniques required for successful developments of the Si ICL approach are briefly discussed with emphasis on two recently developed techniques, i.e. the UHV contactless C–V method and the photoluminescence surface state spectroscopy (PLS3) method. Then, Fermi level pinning phenomenon on MBE-grown surfaces and variously processed surfaces are discussed with their effects on operation and performance of devices. Subsequently, the fundamental theoretical and experimental aspects of the Si ICL technology are reviewed. The topics discussed include quantum state control in Si surface QW, UHV-STM study on atomic arrangements of Si ICL, effects of the initial surface reconstruction, process characterization and optimization by combined use of contactless C–V, XPS and UHV-PL methods. Finally, application of the Si ICL technique to MISFETs, insulated gated HEMTs and passivation of quantum structures are presented and discussed.

Electronic properties of Al xGa 1− xAs surface passivated by ultrathin silicon interface control layer

The photoluminescence surface state spectroscopy (PLS 3) method was applied to a study of the surface state distribution ( N SS), effective surface recombination velocity ( S eff), electron ( E Fn) and hole ( E Fp) quasi-Fermi levels and band bending ( V S) on the Al 0.33Ga 0.67As surface air-exposed and passivated by the Si interface control layer (ICL) technique. Using the detailed measurements of the PL quantum efficiency for different excitation intensities, combined with the rigorous computer simulations of the bulk and surface recombination processes, the behavior and correlation among the surface characteristics under photo-excitation was determined. The present analysis indicated that forming of a Si 3N 4/Si ICL double layer (with a monolayer level control) on AlGaAs surface reduces the minimum interface state density down to 10 10 cm −2 eV −1 and surface recombination velocity to the range of 10 4 cm/s under low excitations.

Photoluminescence characterization of air exposed AlGaAs surface and passivated ex situ by ultrathin silicon interface control layer

Using the photoluminescence surface state spectroscopy (PLS 3) technique, attempts were made to determine the surface state density ( N ss) distribution on Al x Ga 1− x As ( x≈0.3) surfaces passivated by the Si interface control layer (ICL) technique. Air-exposed AlGaAs epitaxial wafers which are technologically important for fabrication of various devices were passivated ex situ by forming a SiO 2/Si 3N 4/Si ICL/AlGaAs structure after the HCl treatment and their photoluminescence behavior was investigated in detail. The result of the PLS 3 analysis indicated that Si ICL-based passivation reduces the minimum interface state density value down to 10 10 cm −2 eV −1 range. Some indication was also obtained that further improvements are possible by using electron cyclotron resonance (ECR)-enhanced N 2 plasma for Si 3N 4/Si ICL interface formation.

Characterization of Interface Electronic Properties of Low-Temperature Ultrathin Oxides and Oxynitrides Formed on Si(111) Surfaces by Contactless Capacitance-Voltage and Photoluminescence Methods

Using contactless capacitance-voltage (C-V), photoluminescence surface state spectroscopy ( PLS3) and X-ray photoelectron spectroscopy techniques, interface electronic properties of ultrathin-insulator films formed on Si (111) surfaces at low temperatures were characterized, paying particular attention to the effect of nitrogen-related plasmas. Hydrogen termination was used as the initial surface treatment. Low-temperature (400° C) thermal oxidation processes produced oxide/Si interfaces with a high-density of interface states that caused limited C-V variation and low PL efficiency. Treatment of low-temperature thermally grown oxides in electron cyclotron resonance (ECR) N2 plasma had no effect on the interface properties. On the other hand, marked enhancement of C-V variation and PL efficiency was achieved at the surface after ECR N2O-plasma oxynitridation at 400° C. The correlation between chemical and electronic properties of the interfaces is discussed.

Contactless capacitance–voltage and photoluminescence characterization of ultrathin oxide–silicon interfaces formed on hydrogen terminated (111) surfaces

Electronic properties of the interfaces between Si and ultrathin (≲10 Å) oxides formed by various low-temperature processes were characterized in contactless fashion, using contactless capacitance–voltage and photoluminescence surface state spectroscopy techniques together with x-ray photoelectron spectroscopy measurement. Hydrogen (H) terminated Si(111) surfaces were used as the initial surface. Ultrathin oxides were formed at low temperatures by chemical oxidation processes (hot HNO3, H2SO4+H2O2), long-time air exposure, and low-temperature oxidation processes below 350 °C. The initial H-terminated surfaces showed presence of Fermi-level pinning at E0=EV+0.65 eV due to high density of amphoteric discrete state probably originating from Si dangling bonds. On the other hand, all the ultrathin oxide–Si interfaces exhibited very limited capacitance variations with voltage at low capacitance levels similar to GaAs metal–insulator–semiconductor systems, and indicated that the Fermi level is pinned near the hybrid orbital charge neutrality level EHO due to presence of interface states with narrow U-shaped continuous distributions. Low-temperature oxidation at 350 °C slightly weakens such pinning. The present work indicates difficulty of realizing unpinned ultrathin oxide–silicon interface by low-temperature processes.

Contactless Characterization of Thermally Oxidized, Air-Exposed and Hydrogen-Terminated Silicon Surfaces by Capacitance-Voltage and Photoluminescence Methods

Contactless and nondestructive characterization of the electrical properties of the free surfaces of single-crystalline silicon wafers is accomplished for the first time by combined use of the contactless metal-insulator-semiconductor (MIS) capacitance-voltage (C-V) technique and the photoluminescence surface state spectroscopy (PLS3) technique. The thermally oxidized, air-exposed and hydrogen-terminated silicon (111) surfaces were investigated. Thick thermally oxidized surfaces showed well-behaved characteristics with a minimum of a broad U-shaped interface state density (N ss) distributions in a range of 1010 cm-2eV-1. On the other hand, the air-exposed Si surface exhibited a GaAs MIS-like behavior with strong Fermi level pinning near the charge neutrality level E HO caused by a narrow U-shaped state distribution. Surprisingly, hydrogen-terminated surfaces showed even stronger Fermi level pinning at E0 = E c - 0.43 eV due to high density of amphoteric discrete state which may be due to silicon dangling bonds.

Determination of Interface State Density Distribution and Surface Recombination Velocity on Passivated Semiconductor Surfaces by Photoluminescence Surface State Spectroscopy

Determination of Interface State Density Distribution and Surface Recombination Velocity on Passivated Semiconductor Surfaces by Photoluminescence Surface State Spectroscopy

Measurement of surface recombination velocity of silicon wafers under sunlight condition by novel photoluminescence surface state spectroscopy

Abstract For a successful realization of super-high efficiency solar cells, reduction of surface or interface recombination is required. Thus, it is important to know the value of the surface recombination velocity ( S ) for the optimization of the passivation technology and for the design of solar cells. In this paper, a photoluminescence (PL) based novel technique for the measurement of the value of S under sunlight is presented, and applied to variously passivated Si surfaces. S was found not to be constant but to depend strongly on the excitation intensity near and above 1 sun condition. The value of S is strongly reduced under concentrated sunlight indicating that concentration of sunlight or use of a thin film is effective for efficiency increase.

In-Situ Characterization of Compound Semiconductor Surfaces by Novel Photoluminescence Surface State Spectroscopy

The recently proposed novel photoluminescence surface state spectroscopy (PLS3) technique is applied for in-situ, non-destructive and contactless characterization of variously processed surfaces of GaAs, InP and InGaAs. Chemically etched, anodized and passivated surfaces, as well as the original as-received surface, give rise to U-shaped surface state density distributions with characteristic charge neutrality energy levels, EHO, which is consistent with the disorder induced gap state (DIGS) model. Annealing of as-received surfaces in hydrogen ambient leads to formation of discrete levels, possibly due to escape of As or P atoms. The effectiveness of a new UHV-based passivation scheme for InGaAs using an ultrathin MBE Si interface control layer (ICL) is also confirmed.