Formation of Three Red-Shift Emissions in Heavily Germanium-Doped P-Type GaAs Grown By MBE
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Formation of Three Red-Shift Emissions In Heavily Germanium-Doped P-Type GaAs Grown By MBE Y.MAKITA-, K.M.MAYER*,
A.YAMADA*,I1.SHIB,\TA:',H.ASAKURA--, and N.KUTSUWADA*...
N.OHNISHI**
,A.C.BEYE-,
"Electrotechnical,Laboratory,1-i-4
Umezono,Tsukuba-shi, 305,Japan. Tokai University,1117 Kitakaname,Hiratsuka-shi,259-12 Japan. Informex Incorporated,Limited,3-15-I0 Hiyoshi,Kohoku-ku,Yokohamashi ,Kanagawa-ken 223,Japan ****Nippon Institute of Technology,4-1 Gakuendai,Miyashiro-machi,Saitama-ken. ABSTRACT Molecular beam epitaxy (MBE) of Ge-doped GaAs was made, in which As4 to Ga flux ratio :y and Ge concentration :[Gel were used as growth parameters. Photoluminescence (PL) spectra at 2K for slightly Ge-doped GaAs revealed that for y =1 the emission of excitons bound to neutral Ge acceptors (A°,X) has the dominant one. With increasing y ,(AO,X) was found to be steeply suppressed and at around y =1.1, (AO,X) was totally quenched. For y higher than 1.1, the emission of excitons bound at neutral Ge donors (D°,X) was gradually enhanced and for y =ll, (DO,X) became the principal one. Through 1 3 van der Pauw measurements, samples with [Gel around IxlOX cMpresented type conversion at around y =1.7. In this series, the sample with y =1.0 indicated a strong specific emission, [g-g], which is formed just below (A0 ,X) and exhibited a strong energy shift towards lower energy sides (red shift) with increasing [Gel. [g-gJ was theoretically attributed to the pairs between excited-state acceptors. Since [g-g] is known to be easily quenched by small amount of donors, the formation of predominant [g-g] for y =1 assures that very low-compensatld p-type GaAs were grown by using this typically amphoteric impurity. We fabricated a series of p-type Ge-doped GaAs by keeping 20 I NA-ND1 as high as Ix10 cm-3 y =1 in which the net hole concentration, was attained. We found four emissions which exhibited significant energy shifts With increasing I NA-ND I . From I NA-ND I -IxlO' 6 cm-3, [g-g] begins 7 3 to appear as a dominant emission and at I NA-ND I ixlO1 cm- , another red shift emission, [g-gjz begins to be formed parralelly on the higher energy side of [g-gj. It is interesting to note that both [g-g] and [g-g]z seem to be totally quenchpd by tie further increase of [Gel. The emission due to band to Ge acceptor,(e,Ge) does not change its central energy until [Gel= 5x1 1O" cm-3 and for larger [Gel it turned into a new broad emission, [-g]18 showing a steep red energy shift. [g-g]a was formed on the higher energy side of (e,Ge) and indicated a systematic blue energy shift with growing 3 [Gel larger than |x]t-"cm- . Ig-gla was theoretically explained to be the emission due to the pairF; between ground-state acceptors.
I NTRODUCT ION Germanium is a typical amphoteric impurity in GaAs but its features are not well documented due to the difficulty of controlling the substitutional sites of Ge atoms. In molecular beam epitaxy (MBE)it was suggested that one can control the location of Ge atoms either at Ga (donor) or As (acceptor) sites by accurate
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