A new room temperature wet chemical digital etching technique for GaAs is presented which uses hydrogen peroxide and an acid in a two‐step etching process to remove GaAs in approximately 15 Å increments. In the first step, GaAs is oxidized by 30% hydrogen peroxide to form an oxide layer that is diffusion limited to a thickness of 14 to 17 Å for time periods from 15 to 120 s. The second step removes this oxide layer with an acid that does not attack unoxidized GaAs. These steps are repeated in succession until the desired etch depth is obtained. Experimental results are presented for this digital etching technique demonstrating the etch rate and process invariability with respect to hydrogen peroxide and acid exposure times.
Etching studies involving citric acid/hydrogen peroxide
false(C6H8O7:H2O2false)
at volume ratios from 0.5:1 to 50:1 were found to provide good selective etching of various III‐V semiconductor materials grown on
normalGaAs
and
normalInP
substrates using molecular beam epitaxy. Both selective and uniform (nonselective) etching regions were found between these material systems by choosing different concentration volume ratios of citric acid/hydrogen peroxide
false(χC6H8O7:1H2O2false)
. Etchant selectivities, defined as a ratio of the etch rates, for the
normalGaAs‐normalbased
materials were measured to be as high as 116 for
normalGaAs/As0.3Ga0.7AS
and 120 for
In0.2Ga0.8normalAs/Al0.3Ga0.7normalAs
. In addition, the
normalInP
system had selectivities of approximately 60 and 100 for
In0.53Ga0.47normalAs/In0.52Al0.48normalAs
and
In0.52Al0.48normalAs/normalInP
, with the highest selectivity of 473 found for
In0.53Ga0.47normalAs/normalInP
. The citric acid/hydrogen peroxide system can be used as a stop etch for
normalInP‐normalbased
devices, as
normalInP
is virtually unaffected by this etchant. Finally, citric acid/hydrogen peroxide can be used to preferentially etch these materials through a photoresist mask, since it does not erode photoresist at any volume ratio.
Citric acid/hydrogen peroxide
false(C6H8O7:H2O2false)
at volume ratios from 0.2:1 to 20:1 was found to provide selective etching between
GaAs1−xSbx false(x=0.15 normalto1.0false)
,
Al0.5Ga0.5normalSb
,
normalInAs
, and various III–V semiconductor materials for use in new
normalGaAs
and
normalInP
based heterostructure transistors and optoelectronic devices. By choosing different concentration volume ratios of citric acid to hydrogen peroxide
false(χC6H8O7:1H2O2false)
, highly selective as well as uniform (nonselective) etching regions were found to exist in these material systems. Etchant selectivities greater than 50 were found for most combinations of the III–V semiconductor materials under investigation, with selectivities of over 100 measured for
normalGaAs/normalGaSb
and
normalInAs/normalGaSb
material combinations, and with selectivities of over 3850 calculated for
normalInAs/Al0.5Ga0.5normalSb
to 13,650 for
normalGaAs/Al0.5Ga0.5normalSb
. The highest overall etch rates were measured for
normalInAs
and the lowest etch rates were found for
Al0.5Ga0.5normalSb
. The etch rate for the
GaAs1−xSbx
materials systematically decreased from the highest etch rate for the smallest Sb mole fraction examined of
GaAs0.85Sb0.15
to the lowest etch rate for
normalGaSb
. The dramatic change in etch rate with citric acid/hydrogen peroxide volume ratio previously observed for the
normalGaAs/normalAlGaAs
material system was also observed for
GaAs0.85Sb0.15
, but this effect was not seen in higher Sb mole fraction alloys of
GaAs1−xSbx
examined.
Al0.5Ga0.5normalSb
and
normalGaSb
were found to have very low etch rates with this etchant system at all volume ratios, making both materials suitable as an etch stop layer for simplified processing in device fabrication. Finally, citric acid/hydrogen peroxide can be used to preferentially etch these materials through a photoresist mask, since it does not erode photoresist at any volume ratio.
Ultrathin (200 Å), highly conductive GaAs and AlAs p/n junction tunnel diodes were fabricated using delta doping. The current carrying capacity of these tunnel diodes is the highest reported to date. The GaAs tunnel junction is capable of handling over 30 A/cm2 at a voltage drop of only 0.02 V, and the AlAs tunnel diode is capable of handling 27 A/cm2 at 0.10 V. These tunnel junctions are useful for interconnecting three-dimensional integrated circuits, integrated optoelectronic devices, and monolithic multijunction solar cells. The delta doping of tunnel junctions to form interdevice ohmic contacts can also be applied to other material systems as well as any devices requiring vertical interconnection.
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