InGaP和GaAs在HCl中的湿蚀刻

1. Introduction 

InGaP, a wide band gap compound semiconductor, is currently attracting a great deal of  attention. Occasionally, somewhat sceptical prognoses of its wider utilization appear,Cl-2 l  yet many authors consider this material to be highly promising for manifold applications in electronic and optoelectronic devices, such as light-emitting diodes, heterobipolar transistors and lasers. C 3-5l

The attractiveness of the InGaP/GaAs heterostructure derives from its energy band  line-up, the valence band offset being markedly larger (AEv = 0.24 - 0.40 eV) than the  conduction band offset (Mc= 0.03 -0.22 eV). This is believed to be more favorable than the energy band structure of the AlGaAs/GaAs heterosystem. In particular, there is intense  interest in the use of InGaP emitters in heterojunction bipolar transistors, which may avoid  the oxidation and deep level problems in AlGaAs.

2. Etch Rate Studies 

In our studies, we used InGaP layers grown on semiinsulating, Cr-doped, (001)­ orientedGaAs substrates by low-pressure metal organic chemical vapor deposition. AsH3 ,  PH3, TMGa (trimethylgallium) and TMin (trimethylindium) were used as the sources of  As, P, Ga and In, respectively. Hydrogen was used as the carrying gas, the total pressure in  the reactor being 5 kPa. The epitaxial layers were prepared at 560°C and the growth rate  was 0.6 µm/hr. The thickness of the layers ranged from 0.36 to 0.70 µm. The nominal  composition of the layers was In0.485Gao.mP.

Figure 1 shows the etch rate of InGaP as a function of the volume content of H3PO4 in  the solution 1 HCI:x H3PO4: 1 H2O2• The etched surface remained smooth. In contrast,  etching in solutions with higher contents of H2O2 resulted in markedly rough surfaces. The  etch rates for GaAs were approximately the same as those for InGaP. Hence, the solution  was suitable for nonselective MESA etching.

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Figure 3 depicts the etch rate oflnGaP with HC1:H3PO4:H2O2 (1:10:1) as a function of  temperature. The increase in temperature from 20 to 44 °C resulted in a rise in the etch rate  by about a factor of three. Assuming thermal activation of etching with a rate proportional  to exp (- E.IRT), where E. is the activation energy, R is the universal gas constant and Tis  the absolute temperature of the etching solution, a least-square fit of the measured data  yielded E. = 9.2 kcal/mole (38.5 kJ/mole). This is a relatively high value, which is typical  of etch processes whose rates are limited by the chemical reaction itself rather than by  dissolution of the reacting products or diffusion of the reacted species towards the etched  surface. Similarly, the smoothness of the etched surface, as observed using optical  microscopy, suggests that the etching process has a reaction limited nature.

3. Conclusion 

We have succeeded in finding an etching solution based on HCl that may be used as an  alternative to the commonly used KKI etchants. By varying the content of HCl in the  solution, one can achieve both nonselective etching, useful for MESA formation, and  strongly selective etching of InGaP over GaAs. An essential advantage of this solution is  that it does not attack gold.