N-type GaAs Epitaxial Layers Research Articles

Linear GaAs Hall generators

A description of GaAs Hall generators, formed in a n-type GaAs epitaxial layer grown on a GaAs semi-insulating substrate by the liquid-phase epitaxial technique, is given. Indium-doped semi-insulating GaAs substrate is used to produce Hall devices with a high sensitivity of 130-160 V A-1T-1 and linearity of <or=1.5% by mitigating effects from the transition layer. These devices have a high temperature stability; they can operate stably at temperatures up to 200 degrees C.

Determination of diffusion length of minority carriers in epitaxial layers by photocurrent spectroscopy

We have determined the minority carrier diffusion length in n-type and p-type GaAs epitaxial layers grown on GaAs substrates as well as on intentionally misoriented Si substrates by photocurrent spectroscopy. It is found that for heteroepitaxial GaAs-on-Si, the minority carrier diffusion length is limited by the amount of dislocation density irrespective of the doping level. The value of dislocation density obtained from diffusion length measurements agrees well with that obtained from the double-crystal x-ray diffraction measurements.

Deep-level transient spectroscopy study of n-type GaAs epitaxial layers grown by close-spaced vapor transport

We have done a deep-level transient spectroscopy study of deep donor traps existing in n-type GaAs epitaxial layers grown by close-spaced vapor transport. All the samples exhibited a bulk trap having an important concentration (≳1014 cm−3), which we have noted ELCS1 and identified with the trap EL12, which was observed in vapor-phase epitaxy materials. Other bulk traps were observed in some samples, but in a weaker concentration (∼1013 cm−3). In other samples, in addition to ELCS1, two more traps were seen; their concentration increased towards the surface. One of them is probably localized near the surface; the other one (ΔEa=0.83 eV, σna=0.8×10−13 cm2) must be identified with the donor trap EL2; it is also present in the bulk, but with a lower concentration.

New metastable defects in GaAs

Two previously unreported metastable defects in n-type GaAs epitaxial layers grown by metalorganic chemical vapor deposition have been identified by deep level transient spectroscopy. These levels, here labeled M3 and M4, have activation energies for thermal emission of electrons of 0.31 and 0.61 eV, respectively. Formation of the M4 center and annealing of the M3 center are observed to take place when a reverse bias is applied to Schottky diodes at elevated temperatures. The reverse transition is observed under zero bias at elevated temperatures (e.g., 400 K). An additional metastable defect, labeled M2, with transformation properties similar to those of the M4 center and an emission activation energy of 0.64 eV, was observed in samples which received a rapid thermal anneal at temperatures of 900 °C and above.

Carrier Concentration and Thickness Measurements of n-Type GaAs Epitaxial Layer by Cell Voltage in Anodization

The carrier concentration and thickness of n-type GaAs epitaxial layers were obtained by cell voltage measurements in anodization, and the results are compared with those obtained by differential C-V measurements. The carrier concentrations in the epi-layer are within the order of those obtained by C-V measurements and the thicknesses of the epi-layer agree with those obtained by C-V measurements. The technique described here enables the carrier concentration and thickness of an epi-layer such as n on an n+ substrate to be determined simply and inexpensively.

Deep level profile studies in chromium radiotracer diffused MOCVD GaAs

The methods of radiotracer diffusion profiling and deep level profiling have been combined to investigate the behaviour of chromium atoms diffused into highly n-type GaAs epitaxial layers. Strong electric fields are found to cause distortion of DLTS profiles for the EL1 centre, but good agreement was obtained using an optically pumped method. A hole trap located at 0.34 eV above the valence, and thought to be associated with the 4+ charge state of Cr, matched the atomic Cr concentration to within a factor of two. It was found that for high temperature diffusions ( m ̃ 1000°C ) most of the Cr atoms act as deep acceptor centres.

Schottky contacts on annealed GaAs

Unimplanted n-type GaAs epitaxial layers have been annealed under the same conditions as those required to activate ion implants. If the duration of the anneal is sufficiently long ( e.g. 10 min at 800°C) acceptor ions accumulate at the surface with a concentration of about 2×10 22 m −3 . Schottky contacts to annealed samples always show increased current densities up to six orders of magnitude greater than those in unannealed layers. This has the effect of lowering the Q values of varactor diodes made out of this material, up to frequencies of 1 GHz.

Amplification of total-reflection-mode acoustic surface waves in n-type GaAs films

The effect of nonparabolicty on the amplification of total-reflection-mode acoustic surface waves in n-type GaAs films has been investigated quantum mechanically in the GHz frequency region. Numerical results are obtained for an n-type GaAs epitaxial layer on a semi-insulating GaAs substrate at 77 K. Results show that the amplification coefficient oscillates with the frequency in the high-frequency region due to the inter-sub-band transitions.

Schottky Contacts on Annealed GaAs

Unimplanted n-type GaAs epitaxial layers have been annealed under the same conditions as those required to activate ion implants. If the duration of the anneal is sufficiently long (e.g. 10 min at 800°C) acceptor ions accumulate at the surface with a concentration of about 2×1022 m−3. Schottky contacts to annealed samples always show increased current densities up to six orders of magnitude greater than those in unannealed layers. This has the effect of lowering the Q values of varactor diodes made out of this material, up to frequencies of 1 GHz.

Residual impurities in high purity GaAs epitaxial layers grown by liquid phase epitaxy

Residual impurities in n-type high purity GaAs epitaxial layers grown by liquid phase epitaxy in graphite and quartz boats were studied. Low temperature near-band photoluminescence and far-IR photoconductivity techniques were used to identify the impurities. The major donor impurity is shown to be silicon rather than the previously reported carbon; this results in higher background density levels, possibly owing to a complex.

Characterization of the interface region in VPE GaAs

“Absolute” electron mobility values in the substrate interface region of n-type GaAs epitaxial layers were investigated. Space-charge scattering was found to be significant near the interface but could be minimized by the sequential growth of layers in one step. Our experimental results suggest that local deviations from stoichiometry may be responsible for the space-charge scattering.

Bulk effects in photoluminescence measurements

It is shown that in some particular cases, photoluminescence measurements may involve not only the thin superficial layer of a semiconductor, but also the bulk of the material. This is the case with a p-type or highly compensated n-type GaAs epitaxial layer deposited on a GaAs substrate. A model of ``secondary luminescence effects'' is given to explain the observed anomalies.

Properties of n type Ge-doped epitaxial GaAs layers grown from Au-rich melts

Degenerate n-type GaAs epitaxial layers doped with Ge are grown from a Au-rich melt. The layers are typical of those produced via the alloy-regrowth process used to make contacts with AuGe or AuSb + 2% Ge. Traps are found in the forbidden gap with one trap induced by the AuGe complex identified at 160 meV above the valence band edge.