H. Fujioka

Electrical characteristics of low temperature-Al 0.3 Ga 0.7 As

In this work, we present electrical characterizations of n+ GaAs/low temperature (LT)-Al0.3Ga0.7As/n+ GaAs resistor structures in which the LT layers are grown at nominal substrate temperatures of 250 and 300°C. The resistivity and Vtfl parameters of these LT-Al0.3Ga0.7As layers are compared with those of LT-GaAs and Al0.3Ga0.7As grown at a normal growth temperature of 720°C. Low-temperature Al0.3Ga0.7As layers exhibit resistivities as high as 1012 ohm-cm, nearly four orders of magnitude higher than that of LT-GaAs, and Vtfl values as high as 45 V, over twice that of LT-GaAs. We also find that the LT-Al0.3Ga0.7As materials grown at 250 and 300°C appear to show opposite and contradictory trends with respect to resistivity and Vtfl. We propose that this result can be explained by residual hopping conduction in the 250°C material. Temperature dependent conductivity measurements confirm the presence of a hopping mechanism in LT-Al0.3Ga0.7As grown at 250°C and yield activation energies of 0.77 and 0.95 eV for LT-GaAs and LT-Al0.3Ga0.7As, respectively.

ANNEALING DYNAMICS OF ARSENIC-RICH GAAS FORMED BY ION IMPLANTATION

We have investigated the annealing temperature dependence of structural and electrical properties in heavily arsenic implanted GaAs which has a similar amount of excess arsenic to low temperature GaAs (LT‐GaAs). The fundamental properties of this material are quite similar to those of LT‐GaAs. High resolution x‐ray diffraction measurements have revealed that it has an increased lattice constant, which is reduced to the value of bulk GaAs by annealing between 300 and 400 °C. Electrical conduction in this material is dominated by hopping between deep states, which is also reduced by annealing above 350 °C. In samples annealed at temperatures ranging from 600 to 850 °C, the dominant electron trap is EL2; it has been confirmed by resistivity measurements with n‐i‐n structures that the Fermi level is pinned by EL2. In samples annealed below 500 °C, the dominant electron trap is not EL2 but the U‐band, although electron paramagnetic resonance measurements show the existence of a large concentration of the ioniz...

Transient current study of low‐temperature grown GaAs using an n‐i‐n structure

The electrical properties of molecular beam epitaxy (MBE) grown low‐temperature GaAs (LT‐GaAs) by current transient spectroscopy (CTS) has been investigated. At least three deep traps have been observed in LT‐GaAs grown at 250 °C and annealed at 600 °C. The deepest level is dominant and has an activation energy of 0.82 eV, which is the same as that of the midgap donor, EL2. This is consistent with the activation energy of resistivity of this sample (0.77 eV), which is close to that for bulk nondoped semi‐insulating wafers. These results indicate that the Fermi level of annealed LT‐GaAs grown at 250 °C is pinned by the deep level at the midgap that is generally ascribed to AsGa antisite defects.

Electrical And Structural Properties Of LT-GaAs: Influence Of As/Ga Flux Ratio And Growth Temperature

The deposition of GaAs by MBE at low temperatures results in a material of unique properties. However, up to now the control and understanding of the electrical and structural properties are unsatisfactory. To investigate the influence of growth parameters on the formation of point defects and electrical properties, the substrate temperature and the As/Ga flux ratio were systematically varied. In a well defined parameter range the lattice expansion was found to be dominated by the formation of As antisite defects. After annealing a high resistivity is obtained independent of the growth conditions. A strong influence of the growth temperature on the band conduction mechanism is observed, whereas a variation of the As/Ga flux ratio induces only slight changes of the temperature dependence of the conductivity.

Control of stoichiometry dependent defects in low temperature GaAs

MBE grown GaAs deposited at low temperatures (LT-GaAs) has already found industrial use as passive buffer layer or gate isolation layer in FETs and as active layer in THz photodetectors. Although LT-GaAs was extensively studied in the past, the role of stoichiometry dependent defects governing the unique properties is not yet fully understood. This study describes the systematic variation of the growth parameters, i.e. growth temperature and As/Ga flux ratio, to control the point defect concentrations. The lattice mismatch between the LT-GaAs layers and the GaAs substrates, which is caused by the incorporation of excess As, decreases with increasing growth temperature and with decreasing As/Ga flux ratio, A linear correlation of the arsenic antisite concentration As/sub Ga/ with the lattice constant is observed. A well defined As/sub Ga/ concentration can be established either by varying the growth temperature or by choosing a certain As/Ga flux ratio, After annealing at 600/spl deg/C all samples exhibit a high electrical resistivity. A single activated behavior with activation energies typical for band conductivity is observed in temperature dependent measurements of the conductivity of n-i-n structures. However, the energy barrier decreases with higher growth temperatures.

Conduction mechanism in arsenic implanted GaAs

We have investigated the electrical properties of heavily arsenic implanted GaAs, which has structural properties similar to low temperature GaAs. The electrical conduction in the lateral direction is dominated by hopping in a defect band and the resistivity after a 600 °C anneal is on the order of 103 Ω cm. However, the resistivity measured on an n‐i‐n structure in the direction perpendicular to the surface is on the order of 109 Ω cm. This huge difference in resistivity can be explained by the lack of an electrical contact to the defect band in the n‐i‐n structure. The activation energy of the resistivity in the n‐i‐n structure is 0.74 eV. This value is close to that for bulk undoped semi‐insulating wafers, in which the Fermi level is pinned at the midgap donor, EL2. A current transient spectroscopy study of this material reveals an electron trap with an activation energy of 0.82 eV, identical to the EL2.

Characterization of low‐temperature AlxGa1−xAs lattice properties using high resolution x‐ray diffraction

Using high resolution x‐ray diffraction techniques, we have studied the lattice parameter behavior of low‐temperature (LT) AlxGa1−xAs as a function of annealing temperature and aluminum content. Similar to LT GaAs, the as‐grown LT AlxGa1−xAs layers exhibit a dilated lattice constant which, upon annealing, contracts to that of ‘‘normal’’ material. The onset of this contraction in LT Al0.3Ga0.7As, however, is found to occur at an annealing temperature nearly 100 °C higher than that required for LT GaAs. In addition, the relative lattice expansion in the as‐grown LT layer is found to be a decreasing function of Al content, ranging from 0.099% for LT GaAs to 0.059% for LT Al0.3Ga0.7As. This is attributed to lower than expected As incorporation in the LT AlxGa1−xAs during growth.

Application of low temperature GaAs to GaAs/Si

Low Temperature grown GaAs (LT-GaAs) was incorporated as a buffer layer for GaAs on Si (GaAs/Si) and striking advantages of this structure were confirmed. The LT-GaAs layer showed high resistivity of 1.7 × 107 ω-cm even on a highly defective GaAs/Si. GaAs/Si with the LT-GaAs buffer layers had smoother surfaces and showed much higher photoluminescence intensities than those without LT-GaAs. Schottky diodes fabricated on GaAs/Si with LT-GaAs showed a drastically reduced leakage current and an improved ideality factor. These results indicate that the LT-GaAs buffer layer is promising for future integrated circuits which utilize GaAs/Si substrates.

Electrical characterization of low‐temperature Al0.3Ga0.7As using n‐i‐n structures

Through temperature‐dependent conductivity measurements, we show evidence of a deep trap level in low‐temperature (LT) Al0.3Ga0.7As layers with an activation energy of ∼0.96 eV. This energy is near that of EL2‐like defects found previously in ‘‘normal’’ epitaxial Al0.3Ga0.7As. It is also considerably larger than the 0.70 eV value typically associated with defects in LT GaAs, which may explain the observed large resistivity (≳1011 Ω cm) in LT Al0.3Ga0.7As. Current transient spectroscopy (CTS) of these samples yields a deep level activation energy of 1.01 eV, in close agreement with the value obtained from conductivity measurements.