Semicond. Scl. Technol. 6 (1991) 1126-1129. Printed in the UK Acceptor states in Pd/n-GaAs devices and effect of hydrogenation P C Srivastava, S Chandra and U P Singh Department of Physics, Banaras Hindu University, Varanasi 221005, India Received 15 February 1991, in final form 11 June 1991, accepted for publication 10 July 1991 Abstract. Pd/n-GaAs devices have been fabricated and electrically characterized, before and after hydrogenation. The technique of hydrogenation is novel in the sense that the hydrogen absorbed in Pd provides a source of hydrogen at room temperature for its injection into GaAs by diffusion. The effective donor density decreases on hydrogenation. The forward bias C-V characteristics show the presence 01two acceptor states at -0.52 and -0.72 eV for the unhydrogenated devices and at -0.83 and -0.92 eV for the hydrogenated devices. The likely origin 01these states is discussed. 1. Introduction . Stlidies on hydrogen incorporation in semiconductor devices is important because of the chemical activity of hydrogen towards native defects and dopant atoms [1-3]. A controlled neutralization of dopants by hydro- gen has resulted in improving the optoelectronic/elec- tronic properties of a wide variety of semiconductors including Ill-V compound semiconductors [4, 5]. Com- mon methods of intentional introduction of hydrogen into III -V compounds are: hydrogen ion implantation and heating in hydrogen plasma. The latter leads to etching and damage in the near surface region while the former introduces a large number of compensating de- fectsin the bulk. A better hydrogenation route would be through molecular hydrogen. However, the decomposi- tion of the H2 molecules at the surface is difficult and generallylimits its introduction into the lattice. We have tried to overcome this limiting proeess by making Pd/ GaAs devices and putting the device in the atmosphere of molecular hydrogen. Palladium adsorbs the molecular hydrogen and stores it as atomic hydrogen. This, in turn, diffusesfrom the palladium filmto the Pd/GaAs interface towards the bulk semiconductor. We performed similar studies [6] on silicon and have shown from the electrical and [-R measurements that hydrogen diffuses to the interface and bulk, resulting in the passivation of the deep and shallow states. In this communication, we have fabricated the Pd/n- GaAs devicesand hydrogenated them in an atmosphere of molecular hydrogen and studied the electrical (1- V, c- V) characteristics. It is observed that the reverse leakagecurrent and the effectivedonor density is reduced after hydrogenation. The C- V characteristics of unhyd- rogenated diodes show the presenceof two deep acceptor 0268-1242/91/121126+04 $03.50 @ 1991 lOP Publishing LId states at -0.52 and -0.72 eV (above the valence band edge).On hydrogenation, the acceptor states are found to be located still deeper at -0.83 and -0.92 eV with a relativelylower concentration and a sharper distribution. The present study thus indicates that hydrogenation reduces both the shallow and deep states. 2. Experimental The samplesused for the study are industrial LECgrown GaAs wafers doped with Si - 1016 cm-3. The wafers are back-contacted with Ni-Ge-Au. Wafers were first cleaned in trichloroethylene and then etched in a solution of NH40H + H202 + H20. Palladium metal films ( - 500 A) have been deposited on top of the wafers in a vacuum of _10-6 Torr by resistive heating technique. Suitable masks have been used to obtain circular metal filmsofarea -1.77 x 10-2cm2on the topof wafers. For hydrogenation, the devices were put in a chamber at room temperature. The chamber is first evacuated to _10-4 Torr. Subsequently, hydrogen gas was intro- duced slowlyinto the chamber so as to achievea pressure of 1 atm. The deviceswere taken out of the chamber after 24 h for electrical measurements. The C- V measurements were carried out using a HP 4277 A multifrequencyLCZmeter. 3. Results and discussion 3.1. 1- V characteristics The current, 1, flowing through the Pd/n-GaAs diode as a function of voltage (V) across it is shown in figure 1