A Structural Study of InP/In 0.61 Ga 0.39 As/InP Quantum Well Using Tem
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311 Mat. Res. Soc. Symp. Proc. Vol. 326. ©1994 Materials Research Society
Sample No
PH3
First GI AsH3
QW growth
Second GI AsH3 PH3
1
0
0
9s
0
2
0
120 s
9s
40 s
5s
3
30 s
40 s
9s
40 s
120 s
4
30s
0
9s
120s
5s
5
120 s
0
9 s
40 s
40 s
0
9s
5s
120s
6
0
312
0
Figure. 2. (002) dark field image of sample 2 grown with 120 sec AsH3 purge during first GI. indicate that for sample 2 second phases are randomly developed instead of forming InGaAs QW. In order to study the structure of the sample 2 in detail, plane view of sample 2 was observed. Typical structure observed in the plane view of sample 2 consists of cellular structure as shown in fig. 3. Inside of cell is defect free area without second phases and it is expected to be InP region. The size of the cell is approximately 1 gm. The second phases identified by moire fringes are formed at the boundary of cell and most of the second phases are developed along the [1101 direction. The area between the cells are heavily deformed with dislocations originated from the boundary of cell (second phases). The composition analysis has been carried out on both inside and boundary of cell using EDX as shown in figs. 4(a) and 4(b), respectively. In and P were detected inside of the cell and In, As, Ga, and P were found on the boundary of cell. Therefore, it can be concluded that inside of the cell is InP and boundary of the cell (second phase) is mixture of InAsi-xPx and Ini-xGaxAsi-yPy phases which will be discussed in below. According to the previous studies, As is very effective in replacing the P atom in the surface of InP substrate and AsH3 purge produces the InAsi-xPx islands with higher As content [3,8]. Therefore, it is expected for sample 2 that InAsi-xPx islands are formed on InP substrate during
Figure. 3. Bright field plane view image of sample 2 grown with 120 sec AsH3 purge during first GI.
313
b
a
InLo,
InLe-
P
P Kox
tLiL4Jx
S.
......
k1
A
.--S_lr,_•_-.......
1.
00
S.....
•- -- !!Ill, ._h._,.,
I
FL tiiL 10.00
IAhk6 i_
Figure. 4. Energy dispersive X-ray spectra from (a) inside of cell and (b) boundary of cell shown in fig. 3. the first GI with 120 sec AsH3 purge. Because of the difference of lattice parameters between InP substrate and InAsi-xPx islands, dislocations are generated from the InAsi-xPx islands forming heavily deformed area as shown in figs. 2 and 3. Even if AsH3 purge has been carried out for 120 sec, the surface of InP substrate is not completely covered by InAsi-xPx islands. In order to grow InGaAs QW, TMGa, TMIn, and AsH3 were introduced simultaneously for 9 seconds. In, As and Ga atoms are seems to be preferentially deposited on InAsi-xPx islands forming In-xGaxAsi-yPy islands instead of forming InGaAs QW. Furthermore, during the second GI with 40 sec AsH3 purge, new InAsi-xPx islands are formed on InP substrate. New InAsi-xPx islands are expected to be nucleated near the Ini-xGaxAsi-yPy islands because the area near Ini-xGaxAsi-yPy islands is heavily deformed. The area marked as'a" in
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