Gregory C. DeSalvo

Wet Chemical Digital Etching of GaAs at Room Temperature

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 A 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 A 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.

Citric Acid Etching of GaAs1 − x Sb x , Al0.5Ga0.5Sb , and InAs for Heterostructure Device Fabrication

Citric acid/hydrogen peroxide (C 6 H 8 O 7 :H 2 O 2 ) at volume ratios from 0.2:1 to 20:1 was found to provide selective etching between GaAs 1-x Sb x (x=0.15 to 1.0), Al 0.5 Ga 0.5 Sb, InAs, and various III-V semiconductor materials for use in new GaAs and InP based heterostructure transistors and optoelectronic devices. By choosing different concentration volume ratios of citric acid to hydrogen peroxide (χC 6 H 8 O 7 :1H 2 O 2 ), highly selective as well as uniform (nonselective) etching regions were found to exist in these material systems

Magneto‐Hall characterization of delta‐doped pseudomorphic high electron mobility transistor structures

Conventional Hall‐effect determination of the two‐dimensional electron gas (2DEG) concentration n2D in pseudomorphic high electron mobility transistor structures is invalid because of interference from the highly doped GaAs cap. Furthermore, the usual methods of dealing with this cap‐interference problem, namely, (1) etching off the cap totally, (2) etching the cap until the mobility reaches a maximum, or (3) growing a separate structure with a thin, depleted cap, in general, give n2D values that are too low. However, we show here that magnetic‐field‐dependent Hall (M‐Hall) measurements can separately determine the carrier concentrations and mobilities in the cap and 2DEG regions, as verified by comparison with a self‐consistent, four‐band, k⋅p calculation and also by electrochemical capacitance‐voltage measurements in structures with different cap and spacer thicknesses.

Depth measurement of doped semiconductors using the Hall technique

A new method using the Hall technique to determine the change in surface layer thickness of doped semiconductors is presented. An equation to calculate the semiconductor thickness change has been determined by comparing the difference in Hall measured sheet carrier concentration and mobility before and after a change in surface layer thickness. Experiments were conducted using a wet chemical digital etch to remove n-type GaAs surface layers having an incremental etch depth control of approximately 15 A in thickness, and the resulting thickness changes were calculated by the Hall technique and measured with a mechanical profilometer. This Hall measurement technique was able to measure changes in surface layer thickness of less than 100 A, and the accuracy of this new technique compared favorably with mechanical profilometer measurements. The new Hall technique method provides accurate measurements of minute thickness changes, and is more accurate than mechanical profilometers for thickness changes less than 150 A.A new method using the Hall technique to determine the change in surface layer thickness of doped semiconductors is presented. An equation to calculate the semiconductor thickness change has been determined by comparing the difference in Hall measured sheet carrier concentration and mobility before and after a change in surface layer thickness. Experiments were conducted using a wet chemical digital etch to remove n-type GaAs surface layers having an incremental etch depth control of approximately 15 A in thickness, and the resulting thickness changes were calculated by the Hall technique and measured with a mechanical profilometer. This Hall measurement technique was able to measure changes in surface layer thickness of less than 100 A, and the accuracy of this new technique compared favorably with mechanical profilometer measurements. The new Hall technique method provides accurate measurements of minute thickness changes, and is more accurate than mechanical profilometers for thickness changes less tha...