Low‐temperature cathodoluminescence spectroscopy was used to investigate the luminescence efficiency of reactive ion etched quantum dots, varying in diameter from 200 μm down to 60 nm. The luminescence efficiency was found to be degraded both with decreasing nanostructure size and with increasing etch depth. A solution to the standard model for diffusion and recombination was applied to the data to determine the surface recombination velocity S. We found that for dots smaller than the diffusion length, the standard diffusion model becomes insensitive to the value of S and fails to predict that there is a size of dot in which the luminescence is completely extinguished. To understand qualitatively the luminescence degradation in etched nanostructures we describe a damage layer thickness ξ. The value of ξ determines the smallest quantum structure that will still emit light. We show that ξ increases with increasing etch depth and is therefore dependent on etching conditions.

Determination of nonradiative surface layer thickness in quantum dots etched from single quantum well GaAs/AlGaAs

Near‐surface (∼1000 A) modification in the net carrier concentration in n‐type InP (n=6×1015–1.5×1017 cm−3) was observed after reactive ion etching (RIE) in Cl‐based (CCl2F2/O2) or organic‐based (C2H6/H2) discharges. The carrier loss is slightly more pronounced in the latter case, due possibly to the creation of deep level, compensating acceptors at greater depths as a result of implantation of the light hydrogen ions. Near‐complete recovery of the initial carrier density occurs after annealing at 500 °C for 30 s. Structural disorder is detected by ion channeling to depths of ∼400 A after C2H6/H2 RIE with a self‐bias of 380 V. This disorder shows significant recovery after 400 °C, 30 s annealing. Current‐voltage measurements on Au Schottky diodes showed ohmic behavior after etching of the InP in a C2H6/H2 discharge, due to the nonstoichiometric surface remaining after RIE. Diodes fabricated on CCl2F2/O2 etched material show only a slight increase in reverse current compared to unetched control samples.

Electrical and structural changes in the near surface of reactively ion etched InP

Structural and electrical damage imparted to InP and In0.72Ga0.28As0.6P0.4 (λg≂1.3 μm) surfaces during CH4/H2 reactive ion etching (RIE) have been examined. X‐ray photoelectron spectroscopy was used to monitor changes in the surface chemistry, Rutherford backscattering spectrometry was used to measure crystallographic damage, and current‐voltage and capacitance‐voltage measurements were made to examine electrically active damage and its depth. Two classes of damage are observed: crystallographic damage originating from preferential loss of P (As) and/or ion bombardment‐induced collision cascade mixing and, for p‐type material, hydrogen passivation of Zn acceptors. Etching at 13.6 MHz, 60–90 mTorr, 10% CH4/H2, and bias voltages of ∼300 V contains gross (≳1%) damage as measured by RBS to within 40 A and electrically active damage to within 200 A of the surface. This is a factor of 3–6 shallower than other RIE processes operated below 10 mT with comparable or higher bias voltages. Acceptor passivation of bot...

Damage to InP and InGaAsP surfaces resulting from CH4/H2 reactive ion etching

We report a breakthrough for selective etching of GaAs over AlxGa1−xAs, x=0.2, layer with a high density plasma source. This result is particularly important for III–V devices such as heterojunction bipolar transistors (HBTs) or high electron mobility transistors (HEMTs). For example, fabrication of HBTs requires a process for selective etching of a GaAs contact layer while stopping on AlGaAs layer. Inductively coupled plasma (ICP) etching with BCl3/SF6/N2/He chemistries showed extremely high selectivity of GaAs over AlGaAs (>200:1) and a photoresist (>10:1). This process also produced excellent sidewall passivation on GaAs with reasonably high rate (>1500 A /min.). Both scanning electron microscope and atomic force microscope data showed AlGaAs etch stop layer was quite smooth after processing. We found that He played a key role in enhancing selectivity and obtaining smooth AlGaAs surfaces. When used with resist masks, addition of N2 into BCl3/SF6 plasma helped formation of passivation on the sidewall an...

https://www.plasmatherm.com/pdfs/papers/17.%20Advanced%20Selective%20Dry%20Etching%20of%20GaAs_AlGaAs%20in%20High%20De.pdf

Advanced selective dry etching of GaAs/AlGaAs in high density inductively coupled plasmas

Near‐surface damage created by Ar+ ion milling in InP and GaAs was characterized by capacitance‐voltage, current‐voltage, photoluminescence, ion channeling, and transmission electron microscopy. We find no evidence of amorphous layer formation in either material even for Ar+ ion energies of 800 eV. Low ion energies (200 eV) create thin (≤100 A) damaged regions which can be removed by annealing at 500 °C. Higher ion energies (≥500 eV) create more thermally stable damaged layers which actually show higher backscattering yields after 500 °C annealing. Heating to 800 °C is required to restore the near‐surface crystallinity, although a layer of extended defects forms in GaAs after such a treatment. No dislocations are observed in InP after this type of annealing. The electrical characteristics of both InP and GaAs after ion milling at ≥500 eV cannot be restored by annealing, and it is necessary to remove the damaged surface by wet chemical etching. For the same Ar+ ion energies the damaged layers are deeper for InP than for GaAs after 500 eV ion milling at 45° incidence angle. Removal of ∼485 and ∼650 A from GaAs and InP, respectively, restores the initial current‐voltage characteristics of simple Schottky diodes.

Ion milling damage in InP and GaAs

We report on the use of a novel technique to study reactive ion etching (RIE) induced damage using multiple quantum wells of 20‐, 40‐, 60‐, and 90‐A widths as in situ probes. Cathodoluminescence (CL) at low temperature, using a finely focused electron beam, allows sensitive determination of the quality of individual quantum wells before and after RIE damage. There is a correspondence between individual luminescence peaks and the depth of the particular quantum well. We can therefore use the CL spectral information to provide a sensitive profile of the depth of RIE induced damage. Various etching conditions and the effects of postetch anneals are examined. Pure Ar sputtering and enhanced chemical etching using CCl2F2/BCl3 at different bias voltages are investigated. Our results reveal that the degree and spatial extent of damage increase with increasing ion energy and decreasing ion mass.

T. Y. Liu

Papers

Investigation of reactive ion etching induced damage in GaAs–AlGaAs quantum well structures