Undoped GaSb Research Articles

Composition and surface deformation variance in highly strained InxGa1−xSb structures on (100) GaSb

InxGa1−xSb is a ternary semiconductor material that offers excellent electronic properties as well as a widely tunable bandgap range (1.7–7.3 μm). However, because of the potentially large lattice mismatch between InxGa1−xSb and GaSb (up to ∼6%), it is inherently difficult to produce large area, high-quality, defect-free InxGa1−xSb epilayers. Studying crystal deformation processes that ultimately enable gliding dislocations in InxGa1−xSb epilayers, as well as the morphologies that result from these processes, is critical for controlling quantum properties in InxGa1−xSb devices. In this study, InxGa1−xSb nanostructures were produced by a solid-source molecular beam epitaxy on undoped GaSb (100) substrates and were examined using various techniques including scanning electron microscopy, energy dispersive spectroscopy, and (micro) Raman spectroscopy. Characterization data demonstrates that with increasing lattice mismatch (compressive strain), there are two distinct regions across the sample, specifically along the 〈110〉 dislocation direction: those with and without epilayer strain. Both regions can be exploited and exhibit high-quality single crystal material, but the strained regions also consist of a wetting layer, strained alloys, and clusters. Epilayer strain, lateral compositional gradients, and biaxial stress were analyzed as a function of Raman shift in these layers and revealed dependencies on the influence of dislocation slip planes.

Heavy and light hole transport in nominally undoped GaSb substrates

In this work, we report results of a study of electronic transport in nominally undoped p-type GaSb wafers typically employed as substrate material for the epitaxial growth of InAs/GaInSb type-II superlattices. Magnetic field dependent Hall-effect measurements and high-resolution mobility spectrum analysis clearly indicate p-type conductivity due to carriers in both the heavy and light hole bands. The extracted hole concentrations indicate a thermal activation energy of 17.8 meV for the dominant native acceptor-like defects. A temperature-independent effective mass ratio of 9.0 ± 0.8 was determined from the ratio of measured heavy and light hole concentrations. Over the 56 K–300 K temperature range, the light hole mobility was found to be 4.7 ± 0.7 times higher than the heavy hole mobility. The measured room temperature mobilities for the light and heavy holes were 2550 cm2/Vs and 520 cm2/Vs, respectively.

Native point defects in GaSb

We have applied positron annihilation spectroscopy to study native point defects in Te-doped n-type and nominally undoped p-type GaSb single crystals. The results show that the dominant vacancy defect trapping positrons in bulk GaSb is the gallium monovacancy. The temperature dependence of the average positron lifetime in both p- and n-type GaSb indicates that negative ion type defects with no associated open volume compete with the Ga vacancies. Based on comparison with theoretical predictions, these negative ions are identified as Ga antisites. The concentrations of these negatively charged defects exceed the Ga vacancy concentrations nearly by an order of magnitude. We conclude that the Ga antisite is the native defect responsible for p-type conductivity in GaSb single crystals.

The optical and electrical properties of AP-MOVPE GaSb grown using TEGa and TMSb

High quality undoped metal-organic vapour phase epitaxial (MOVPE) GaSb layers have been grown on GaAs using the trimethylantimony/triethylgallium (TMSb/TEGa) precursor combination at 550°C and atmospheric pressure. The effects of the TMSb to TEGa flux ratio (i.e. V/III ratio) on the surface morphology and optical and transport properties of these layers have been investigated. The transport properties were found to be comparable to the best reported for un-doped GaSb grown using the same precursors at low reactor pressures. Two models (using either two monovalent acceptors or one divalent acceptor) were used to estimate the density of native acceptors and the ionization energy of the acceptors in GaSb. These models showed the shallow acceptor activation energy or first ionization energy to be ∼30 meV (falling within the reported range of 20–40 meV). The ionization energy of the deeper acceptor or second ionization of the level was determined to be ∼120 meV.

Rapid Thermal Annealing on GaSb Thin Films Grown by Molecular Beam Epitaxy on GaAs Substrates

Unintentionally doped GaSb films grown by Molecular Beam Epitaxy (MBE) on GaAs (001) substrates were annealed under different temperatures and time. It was found that the rapid thermal annealing (RTA) process can improve the optical properties. By changing annealing temperature and time, the optimized annealing temperature and times are found to be 650°C and 30s, respectively. Point defects and dislocations are two major kinds of defect in undoped GaSb thin films grown by MBE on GaAs (001) substrates.

Acceptors in undoped GaSb; the role of vacancy defects

The conventional lifetime setup was used to study Czochralski grown unintentionally p- and n- type ([n] ≈ 6 × 1017cm−3) GaSb bulk samples. Several approaches were used to analyze the data. However, it was not possible to successfully analyze the obtained spectrums with the conventional trapping model. From the analyzed data it was derived that the reason for p-type behavior of GaSb was not VGa. Additionally, the role of gallium vacancy was studied and it's effect to lifetime values are shortly discussed.

Contactless electroreflectance study of the Fermi level pinning on GaSb surface in n-type and p-type GaSb Van Hoof structures

Contactless electroreflectance (CER) has been applied to study the Fermi-level position on GaSb surface in n-type and p-type GaSb Van Hoof structures. CER resonances, followed by strong Franz-Keldysh oscillation of various periods, were clearly observed for two series of structures. This period was much wider (i.e., the built-in electric field was much larger) for n-type structures, indicating that the GaSb surface Fermi level pinning position is closer to the valence-band than the conduction-band. From analysis of the built-in electric fields in undoped GaSb layers, it was concluded that on GaSb surface the Fermi-level is located ∼0.2 eV above the valence band.

Influence of Growth Conditions and Doping on Physical Properties of Gallium Antimonide Single Crystals

Gallium antimonide (GaSb) single crystals were grown by modi ed Czochralski method integrated with in situ synthesis in a owing atmosphere of pure hydrogen. The in uence of charge material purity as well as other technological parameters on GaSb crystals quality was investigated. High purity undoped GaSb single crystals were grown with residual acceptors concentration < 1.4 × 10 cm−3 and high mobility ≈ 690 cm/V s (at 300 K). P -type GaSb crystals were doped with silicon (carrier concentration up to 2 × 10 cm−3) and with zinc (up to 1× 10 cm−3). Tellurium doped n-type GaSb single crystals were obtained with concentration up to 2× 10 cm−3. Electrical parameters were investigated by the Hall measurements (300 K and 77 K). Temperature dependent Hall measurements (10 ÷ 300 K) were used to compare the quality of undoped GaSb (obtained from Sb of di erent purity). Dopant concentration was estimated by glow discharge mass spectroscopy analysis. Axial and radial distribution of carrier concentration were investigated especially for Te-doped crystals (low segregation coe cient of Te in GaSb). Great contribution of compensation and self-compensation mechanisms is shown especially for the beginning part of grown crystals and for low Te-doping level. Radial distribution of physical properties for crystals grown in ⟨100⟩ direction is not axisymmetrical especially for doped GaSb crystals.

Native point defect energetics in GaSb: Enablingp-type conductivity of undoped GaSb

The energetics of native point defects in GaSb is studied using the density-functional theory within the hybrid functional scheme (HSE06). Our results indicate that the GaSb antisite has the lowest formation energy and could thus be the acceptor defect responsible for the p-type conductivity of undoped GaSb. We find also that the SbGa antisite has a remarkably low formation energy in Sb-rich growth conditions and it should act as a donor for all Fermi level positions in the band gap. However, we suggest that the structural metastability of the SbGa antisite or extrinsic point defects, namely carbon and in particular oxygen, may neutralize its compensating character.

Defect of Te-doped GaSb layers grown by molecular beam epitaxy

In this paper we present the results of positron annihilation doppler broadening spectroscopy(PADB),X-ray diffraction spectra(XRD),and atomic force microscopy(AFM) measurements on the undoped GaSb and Te-doped GaSb films grown on GaAs substrate by molecular beam epitaxy(MBE).Research shows that the S parameter is smaller in GaSb film than the bulk material.The defects in the Te-doped N-type semiconductor GaSb obtained by MBE are mainly vacancies and impurity atoms instead of complex defects.

Photopyroelectric back detection configuration for thermal diffusivity measurement of undoped and doped GaSb semiconductors

Photopyroelectric technique in back detection configuration (BPPE) was used to investigate thermal diffusivity measurement of undoped and doped GaSb bulk samples. A theoretical model was developed and specific design of pyroelectric sensor based on PVDF film of 25μm thickness was constructed. The methodology is based on a designed back photopyroelectric detection cell and thermal diffusivity value is obtained directly as a result of a scan of the BPPE phase and amplitude signal as a function of square root modulation frequency.This method involves the thermally thick limit of the pyroelectric signal in the standard BPPE. To avoid the conventional requirement for set-up transfer function a signal normalization procedure is implemented.Obtained thermal diffusivity coefficients by means of this technique are 16.7 ± 0.5*10−6 m2s−1, 6.3 ±0.3 *10−6 m2s−1, and 7.3 ± 0.2 *10−6 m2s−1 respectively for undoped GaSb, Te- doped GaSb and Zn-doped GaSb semiconductors.By studying samples of GaSb with different types of doping (doping with Te and with Zn) we notice a change in the thermal diffusivity function of doping.

Impurity‐band conduction in polycrystalline films of GaSb and GaSbAs grown by molecular‐beam deposition

AbstractPolycrystalline films of undoped GaSb, GaSb0.86As0.14, and GaSb0.8As0.2 were grown on glass substrates by molecular‐beam deposition. Hall‐effect measurements were performed in the temperature range of 10‐400 K. Temperature dependences of concentration and mobility of holes at low temperatures were well explained in terms of two‐band conduction consisting of impurity‐band and valence‐band conduction which is limited predominantly by potential barriers at grain boundaries. The procedure for analyzing the Hall‐effect data is extended to be applicable to the sample involving not only the impurity band but also an additional deep acceptor level as well as a compensating donor level, so that the experimental results at high temperatures can also be well simulated. (© 2012 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Growth and Characterization of Unintentionally Doped GaSb Nanowires

GaSb nanowires were synthesized on c-plane sapphire substrates by gold-mediated vapor–liquid–solid (VLS) growth using a metalorganic chemical vapor deposition process. A narrow process window for GaSb nanowire growth was identified. Chemical analysis revealed variations in the catalyst composition which were explained in terms of the Au-Ga-Sb ternary phase diagram and suggest that the VLS growth mechanism was responsible for the nanowire growth. The nominally undoped GaSb nanowires were determined to be p-type with resistivity on the order of 0.23 Ω cm. The photoluminescence was found to be highly dependent on the V/III ratio, with an optimal ratio of unity.

Investigation of thermal diffusivity of doped and undoped GaSb by the Photothermal Deflection Technique

In this paper we present a new method based on the photothermal deflection and applied to bulk semiconductors in order to determine the thermal diffusivity. The sample is placed in the air and heated with a modulated light beam generated by a Halogen Lampe instead of traditionally a laser beam power. The advantage of this method lies in its simplicity and great sensitivity to the thermal diffusivity variation of the sample. By studying samples of GaSb with different types of doping (doping with Te and with Zn) we notice a change in the thermal diffusivity function of doping.

Photothermal investigations of doping effects on opto-thermal properties of bulk GaSb

GaSb is a direct gap semiconductor (0.72 ev) having good carriers motility and significant electro-optical potential in the near IR range. As substrate or active layer, GaSb can be employed in conjunction with many semiconductors such as (AlGa)Sb or In(AsSb) and has interesting hetero junction potential for detectors, lasers and quantum well structures. The aim of this work is to investigate the influence of doping on the opto-thermal properties (optical absorption, refractive index and thermal diffusivity) of doped and undoped GaSb bulk throw, the phothermal deflection and spectroscopic reflectivity. It is found that absorption below the gap and thermal diffusivity increases with doping concentration.

적외선검출소자를 위한 GaSb 결정 및 MBE로 성장한 Gasb/SI-GaAs 박막의 진성결함에 관한 연구

Sb에 기초한 응력 초격자 적외선검출소자의 구성 물질인 도핑하지 않은 기판 GaSb 결정과 GaSb/SI-GaAs 박막에 잔존하고 있는 진성결함 (intrinsic defect)을 비교 조사하였다. 상온 근처 (250 K)까지 광여기 발광 (PL)을 보이는 GaSb 결정에서의 발광 에너지의 온도의존성으로부터, 밴드갭 에너지에 관한 경험식인 Varshni 함수의 파라미터 (<TEX>$E_o$</TEX>, <TEX>$\alpha$</TEX>, <TEX>$\beta$</TEX>)를 결정하였다. GaAs 기판 위에 성장된 이종 GaSb 박막에서는 GaSb 주요 진성결함으로 알려져 있는 29 meV의 이온화 에너지를 가지는 위치반전 (antisite) Ga ([<TEX>$Ga_{Sb}$</TEX>]) 결함과 함께 위치반전 Sb ([<TEX>$Sb_{Ga}$</TEX>])와의 복합결함 ([<TEX>$Ga_{Sb}-Sb_{Ga}$</TEX>])과 관련된 것으로 분석된 732/711 meV의 한 쌍의 깊은준위 (deep level)가 관측되었다. PL의 온도 및 여기출력 의존성을 분석하여, Sb-rich상태에서 성장된 GaSb 박막에서는 잉여 Sb의 자발확산 (self-diffusion)에 의하여 치환된 위치전도 [<TEX>$Ga_{Sb}$</TEX>] 및 [<TEX>$Sb_{Ga}$</TEX>]가 결합하여 [<TEX>$Ga_{Sb}-Sb_{Ga}$</TEX>]의 깊은준위를 형성하는 것으로 해석되었다. We have investigated the intrinsic defects remaining in epitaxial GaSb layers grown on SI-GaAs substrates compared to those in bulk GaSb crystal substrate, which is a basic material of Sb-based strained-layer superlattice infrared photodetectors. From the functional dependence of the band-to-band transition energy of the photomuminescence (PL) spectra observing up to near room-temperature (250 K), the temperature parameters of [<TEX>$E_o$</TEX>, <TEX>$\alpha$</TEX>, <TEX>$\beta$</TEX>] of undoped GaSb crystal are determined by using the Varshni empirical equation describing the temperature variation of the bandgap energy. Additionally to the antisite-Ga ([<TEX>$Ga_{Sb}$</TEX>]) with an ionization energy of 29 meV that is well known to a major intrinsic defect in GaSb, epitaxial GaSb layers show a pair of deep states at the emission energy of 732/711 meV that may be related with a complex of two antisite-Ga and antisite-Sb ([<TEX>$Ga_{Sb}-Sb_{Ga}$</TEX>]). Based on the analysis of the temperature and the excitation-power dependences of PL, it suggests that excess-Sb substitutes Ga-site by self-diffusion and two anti sites of [<TEX>$Ga_{Sb}$</TEX>] and [<TEX>$Sb_{Ga}$</TEX>] could form as a complex of [<TEX>$Ga_{Sb}-Sb_{Ga}$</TEX>] in GaSb epilayers grown under Sb-rich condition.

Temperature and doping dependence of electron spin relaxation in GaSb

Electron spin relaxation times in n-doped as well as in nominally undoped bulk GaSb are measured with time-resolved circular dichroism and Faraday rotation induced by 1.55 µm, 150 fs pulses. Degenerately n-doped samples are characterized by ultrashort relaxation times of ∼2 ps. In contrast, we find much larger time constants and a strong temperature dependence of the spin relaxation time in moderately n-doped and undoped GaSb. The longest spin relaxation time is found to be ∼30 ps for an undoped sample at temperatures below T = 50 K. Many aspects of the results can be attributed to the large spin–orbit coupling in GaSb, consistent with the D'yakonov–Perel' theory of spin relaxation. In addition, magneto-optical measurements reveal an effective electronic Landé factor of |g*| = 9 ± 1.

MBE growth of II–VI materials on GaSb substrates for photovoltaic applications

The II–VI materials lattice matched to GaSb substrates are desirable for ultrahigh-efficiency multijunction solar cells. This paper reports the growth of ZnTe and ZnCdTe/ZnTe quantum wells on undoped GaSb (1 0 0) substrates using molecular beam epitaxy. During growth, in situ reflection high-energy electron diffraction shows fast and smooth transition from GaSb surface to ZnTe surface. Post-growth structural characterization using X-ray diffraction and high-resolution transmission electron microscopy reveals very low-defect density, i.e. high crystalline quality. Visible photoluminescence is observed from 10 to 300 K.

Thermostable tensoresistors of Co doped GaSb–FeGa 1.3 eutectic composites

The microstructure and tensoresistive properties of GaSb–FeGa 1.3 eutectic composites doped with 0.1% Co have been investigated. It was found that the Co impurity atoms mainly accumulate in the metallic inclusions. The length of the inclusions in GaSb–FeGa 1.3〈Co〉 was measured to be about half of those in undoped GaSb–FeGa 1.3 eutectics. The tensometric characteristics of gauges based on GaSb–FeGa 1.3〈Co〉 have been found to be more thermostable than undoped samples.

Measurement of the GaSb surface band bending potential from the magnetotransport characteristics of GaSb–InAs–AlSb quantum wells

Low-temperature magnetotransport measurements on GaSb∕InAs∕AlSb coupled quantum well structures with a GaSb cap layer and self-consistent calculations of their electronic structure have led to the determination of the Fermi level at the surface, EFS, of undoped molecular-beam-epitaxy-grown GaSb. EFS is pinned around 0.2eV above the top of the GaSb valence band when the GaSb cap layer width is greater than around 900Å. For smaller GaSb cap widths, EFS decreases with the GaSb width. The undoped GaSb∕InAs∕AlSb heterostructure’s Fermi level is determined by bulk donor defects in the AlSb layer adjacent to the InAs quantum well.