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An effective gate recess etch process has been applied to AlGaN/GaN modulation-doped field-effect transistors (MODFETs), utilizing low power Cl2 reactive ion etching. In comparison to GaAs-based materials, GaN shows a greater robustness to ion damage under ion bombardment at very low ion energies (

Damage introduced from sputtering deposition, electron-beam evaporation, and thermal evaporation were investigated with an InGaAs/GaAs strained quantum well structure. This strained quantum well structure was found to be a more sensitive probe of damage, revealing metallization-induced damage where none was found using comparable lattice-matched quantum wells. The damage was found to vary with deposition method, deposition rates, or even different metal sources used. Noticeable degradation of the photoluminescence of the strained quantum well was observed after a thin layer (∼100 A) of metal was deposited.

A study of the effects of reactive ion etching on molecular beam epitaxy grown (CdxZn1−xSe/ZnSe) strained quantum well (QW) samples using low temperature photoluminescence reveals a blue shift in the characteristic peak position of the 8 nm QW when exposed to plasmas of H2, D2, or He. Based on experimental results we suggest that this blue shift is a result of ion induced damage interacting with strain present in the as-grown QW. The QW is compressively strained at the interface with additional local strains in the QW lattice due to its random ternary alloy composition. The shallowest QW samples exhibit a peak in the blue shift as a function of bias voltage, with a reduced blue shift seen at high voltages.

Radiation-enhanced diffusion of dry-etch damage observed from experiments has been further characterized with Schottky diodes and deep level transient spectroscopy (DLTS) measurements. The use of DLTS spectra to monitor the effects of changes in ion dose rate and the application of laser radiation shows that the ion-induced defects having high diffusivities during ion-assisted processes are basically associated with the components of primary point defects, such as interstitials and vacancies. The properties of ion-induced traps obtained from DLTS measurements may provide us with some information to refine our model on the low-energy ion-induced damage.

There has been steady progress in understanding the propagation of low‐energy, ion‐induced damage into semiconductor substrates. The availability of specifically designed heterostructure substrates allows us to trace the profile of damage into the material. A number of experiments, together with theoretical simulations, have confirmed the important role played by fortuitous channeling of ions, deep into the material (e.g., >1000 A deep for incident ions energies ∼300 eV). Recent experiments have also shown the importance of rapid diffusion of ion‐created defects. Using a model that includes the effects of both channeling and defect diffusion, channeling and diffusion in ion damage (CHANDID), we have deduced a room‐temperature diffusion constant of D∼1×10−15 cm2/s. This is an extremely high value for diffusion at room temperature, and is more characteristic of diffusion taking place at temperatures of a few hundred to a few thousand degrees centigrade. One cause of this high value of D may be attributed to radiation enhanced diffusion: the creation of excess electrons and holes during the etch process whose subsequent nonradiative recombination transfers momentum to the defects. Preliminary experiments, which monitor the effects of above band‐gap illumination during ion bombardment, validate this picture. Such understanding, of intrinsic importance, can be used to design material and device structures in which the effects of ion damage may be mitigated.

We have investigated the radiation enhanced diffusion of ion defects during reactive ion beam etching of GaAs and InP, using the multiple quantum well (MQW) probe technique. During low energy (sub‐keV) Ar+ ion exposure, illumination with light of energy above the band gap can substantially reduce the photoluminescence efficiency of MQW samples, relative to those which were not laser illuminated; the degradation of luminescence efficiency increases with the intensity of the light. Illumination with light of energy below the band gap produces a slight increase in the damage profiles. The observation of enhanced defect diffusion due to optical radiation in our studies suggests that in ion‐assisted etching of semiconductors, the generation of excess electron‐hole pairs and their subsequent recombination can play an important role in the propagation of defects into the substrate.

A simple model, including both channeling and diffusion effects, has been developed for the understanding of the mechanism of low‐energy ion‐induced damage. This model provided much better agreement with our experimental data, and yields a value for the effective diffusivity of defects during ion bombardment as ∼3×10−15 cm2/s. The numerical results support our experimental data that diffusion of defects, even at room temperature, plays an important role in determining the profile of ion‐induced damage and suggests that some enhancement of defect diffusion occurs during ion bombardment. In addition, since the majority of defects are located in the near‐surface region (within ∼50 A of the surface), even modest etch removal of the surface can dramatically alter the damage profile. Therefore, surface removal has also been considered in our model to find the influence of etch rate on the ion damage profile.