Surface Characteristics of Etched and Non-etched Silicon 

Germanium (SiGe)/Si Graded Structure with Varying Ge 

Concentration Grown by Ultra-high Vacuum (UHV)/

Chemical Vapor Deposition (CVD) for Optoelectronic and 

Power Conversion Applications

by Fred Semendy, Patrick Taylor, Greg Meissner,

and Priyalal Wijewarnasuriya

ARL-TR-6128 September 2012

Approved for public release; distribution unlimited. 
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Army Research Laboratory 

Adelphi, MD 20783-1197 

ARL-TR-6128 September 2012 

Surface Characteristics of Etched and Non-etched Silicon 

Germanium (SiGe)/Si Graded Structure with Varying Ge 

Concentration Grown by Ultra-high Vacuum (UHV)/

Chemical Vapor Deposition (CVD) for Optoelectronic and 

Power Conversion Applications 

Fred Semendy, Patrick Taylor, Greg Meissner, 

and Priyalal Wijewarnasuriya 

Sensors and Electron Devices Directorate, ARL 

Approved for public release; distribution unlimited. 
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Surface Characteristics of Etched and Non-etched Silicon Germanium (SiGe)/Si 

Graded Structure with Varying Ge Concentration Grown by Ultra-high Vacuum 

(UHV)/Chemical Vapor Deposition (CVD) for Optoelectronic and Power 

Conversion Applications

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14. ABSTRACT

Graded high-quality silicon germanium (SiGe) epitaxial layers were grown on n-type Si with varying Ge concentration using 

low-temperature ultra-high vacuum (UHV)/chemical vapor deposition (CVD). The graded layers were grown on Si substrates 

followed by a final growth of doped Si1–xGex with varying percentage of Ge for comparison study. Various techniques, 

including atomic force microscopy (AFM), optical reflectance, and transmission were used to characterize the surface and 

structural quality of the materials. The investigation also included for the first time the reflectivity and absorbance of etched 

black silicon-germanium (Si1–xGex). Black Si1–xGex was produced by metal enhanced chemical etching using nanometer-scale 

gold particles as the catalyst and hydrogen fluoride (HF):hydrogen peroxide (H2O2):acetic acid (CH3COOH) as the etchant. The 

etched surface was black and textured, and showed strong suppression of reflectivity and enhanced absorption in the nearinfrared, which are consistent with Si1–xGex becoming highly surface-textured due to metal catalysis and wet etching. Lowering 

reflection and enhancing absorption in Si1–xGex is an important milestone towards practical, extended wavelength (~2 μm) 

electro-optical applications. There is good evidence that varying Ge concentration affects the surface properties across different 

techniques in determining layer composition and thickness. The surface root-mean-square roughness before etching measured 

by AFM for all the samples indicate very smooth surfaces.

15. SUBJECT TERMS

SiGe/Ge, etched, UHV/CUD, black SiGe/Si, surface properties

16. SECURITY CLASSIFICATION OF: 

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Fred Semendy

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iii

Contents 

List of Figures iv

Acknowledgments v

1. Introduction 1

2. Experiment 3

3. Results and Discussion 5

4. Conclusion 10

5. References 11

List of Symbols, Abbreviations, and Acronyms 13

Distribution List 15
iv

List of Figures 

Figure 1. Epitaxial SiGe layers on Si (001) with a pseudomorphic layer on the left and a 

partially relaxed layer on the right. ............................................................................................2

Figure 2. (a) Structure of the grown material, (b) 12% GeSi on graded GeSi on the Si 

substrate, (c) 30% GeSi on graded GeSi on the Si substrate, and (d) 40% GeSi on graded 

GeSi on the Si substrate with all layers n+ doped. ....................................................................4

Figure 3. Experimental procedure for the nano catalyst formation on the SiGe surface. ...............5

Figure 4. Nomarski images of the surfaces of three very thick p-type samples: (a) 15% Ge, 

(b) 30% Ge, and (c) 50% Ge at 50×. ........................................................................................6

Figure 5. Normaski images of the surfaces of three n-type samples: (a) 12% Ge, (b) 30% Ge, 

and (c) 40% Ge at 50×. ..............................................................................................................7

Figure 6. AFM images of the surfaces of three samples: (a) 12% Ge, (b) 30% Ge, and (c) 

40% Ge.......................................................................................................................................7

Figure 7. The step height from AFM images of the surfaces of three samples: (a) 12% Ge, 

(b) 30% Ge, and (c) 40% Ge.....................................................................................................8

Figure 8. Etch rate of Si1–xGex in HF:H2O2:CH3COOH (1:2:3). ....................................................8

Figure 9. %R of unetched and etched samples: (a) Si0.85Ge0.15, (b) Si0.70Ge0.30, and (c) 

Si0.50Ge0.50..............................................................................................................................9

Figure 10. The surface texture pattern of the sample Si0.70Ge0.30. ................................................10
v

Acknowledgments 

We would like to thank Dr. Mayank Bulsara at the Dept. of Materials Science and Engineering at 

the Massachusetts Institute of Technology for providing the high-quality black silicongermanium (Si(x)Ge(1–x)) heteroepitaxial layers for this work. 
vi

INTENTIONALLY LEFT BLANK.
1

1. Introduction 

Bandgap engineering with the well-established silicon (Si) technology has generated interest in 

combing Si with silicon germanium (SiGe) alloys, which provides a technological promise of 

new electronic, optoelectronic, and power conversion efficient devices (1). In the past few years,

attempts such as “blackening” the surface of Si1–xGex by metal enhanced etching (MEE) have 

been made at the U.S. Army Research Laboratory (ARL) to improve the optical property of 

absorption beyond 1.4 μm, which may make it a useful material of choice for infrared (IR) 

detection compared to expensive indium gallium arsenide (InGaAs) (2). 

Semiconductor heterostructures such as SiGe/Si greatly enhance the range of possible device 

configuration and open the door for new phenomena such as tunneling, tenability of absorption, 

real space-carrier transfer, two-dimensional (2-D) carrier gases, and quantum size effects. Over 

the past several years, advances in SiGe technology have shown impressive potential for the 

development of advanced Si-based electronic and optical devices, and thermoelectric generators 

incorporating Ge. In particular, SiGe heterostructure technology is beginning to rival III–V 

semiconductors in many applications (3–5). Heteroepitaxy is the epitaxial growth of multiple 

dissimilar materials to form a layered heterojunction (HJ). HJs can be used to drive both carriers 

in to the same volume; separate carriers from the parent dopant atoms; or form local 

accumulation or depletion regions independent of doping. This behavior contrasts sharply with 

homojunctions. HJ devices offer an immensely larger array of device configurations and has 

become the basis for the band gap engineering (6). However, HJ devices are very rare because 

the dominant semiconductor Si is not compatible with any other semiconductor. Therefore, 

heterojunction devices have been based mostly upon III-V, and II-VI compound semiconductors 

materials. However, these materials are very expensive with inferior thermal and mechanical 

properties, leading to lower crystalline perfection. 

Heterostructures are based on differences in the electronic bandstructure of the component 

semiconductors. All of the common semiconductors are based on four fold tetragonally oriented 

bonds in a diamond like configuration. Adding any dopant from the III- or V- to Si can cause 

segregation (7, 8). This occurs because the condensing Si atom has a finite probability of 

exchanging positions with a surface dopant atom. Another problem is that Si-based 

heterostructures may not grow as flat layers. This is due to the size difference as well as the 

character of the bonds being covalent versus polar with respect Si, e.g., gallium phosphide (GaP) 

has a small lattice misfit with Si, but grows as three-dimensional (3-D) islands because of 

bonding differences. Hence GaP/Si grows as isolated 3-D islands (9). With a continuous effort, 

the islands will coalesce and form continuous layers. In general, such materials will be highly 

doped and usually with a thickness greater than 1 μm. Fortunately, Ge can be used for growing 
2

misfit accommodated SiGe/Si heterostructures to form HJ devices: the natural column IV 

pairing of Si is with Ge. Ge has an atomic spacing of 4.2% larger than that of Si, so lattice misfit 

is one issue that needs to be managed to obtain low defect-density. To that end, in this work we 

pursue a special pseudomorphic growth mode to grow Si(x)Ge(1–x) alloys on Si with low defect 

density 

Figure 1 gives a depiction of the pseudomorphic layer on the left and a partially relaxed layer on 

the right. 

Figure 1. Epitaxial SiGe layers on Si (001) with a pseudomorphic layer on the left and a 

partially relaxed layer on the right.

A SiGe layer pseudomorphically grown on a Si substrate is elastically strained. The in-plane 

lattice parameter is equal to that of Si, and thus, is smaller than the lattice parameter of the bulk 

SiGe layer. Likewise, the out-of-plane lattice constant is larger than that of the bulk SiGe alloy. 

When the film thickness exceeds the critical thickness for pseudomorphic growth, the mismatch 

strain is relieved by the formation of misfit dislocations—as shown in figure 1 on the right side. 

At low mismatch strain, Si1–xGex /Si (001) structures relax by the introduction of 60° 

dislocations. Hence, the goal for fabricating good quality reliable devices is to use a defect-free 

device structure on the substrate. 

Many attempts have been made in growing defect-free structures by introducing compositional 

grading (10, 11) and low-temperature buffer layers (12, 13). These two techniques are highly 

successful leading to reductions in density of threading dislocations by 4–5 orders of magnitude. 

However, irrespective of these methods to reduce dislocations, strain relaxation results in an

undulation in the surface morphology (14) known as “crosshatch” pattern (15). The crosshatch 

is characteristic of low misfit regime—with a lattice mismatch less than 2%. It has been 

observed in almost all heterostructures. The crosshatch-related surface roughening can affect 

Si Substrate 

 HeteroInterface 

SiGe Layer 

60° misfit

dislocations

Pseudomorphic Layer Partially relaxed layer layer

Si Substrate 

 HeteroInterface 

SiGe Layer 

60° misfit

dislocations

Pseudomorphic Layer Partially relaxed layer layer

Si Substrate 

 HeteroInterface 

SiGe Layer 

60° misfit

dislocations

Pseudomorphic Layer Partially relaxed layer layer

Si Substrate 

 HeteroInterface 

SiGe Layer 

60° misfit

dislocations

Pseudomorphic layer Partially relaxed layer 
3

carrier mobility and the quality of quantum structures grown on such surfaces. It is not 

compatible with planar integrated circuit technologies, the major driver for applications. 

To eliminate the defects, it is therefore very important to understand their structure and origin. 

Atomic force microscopy (AFM) and transmission electron microscopy (TEM) techniques are 

used to study evolution of surface morphology during strain relaxation and the mechanism by 

which dislocations give rise to crosshatching. Two types of models have been proposed (16). In 

the first model, the formation of crosshatch patterns is caused by surface diffusion during growth 

in response to the inhomogeneous strain fields arising from the network of misfit dislocations. 

The second model suggests that crosshatching results from the surface steps at the intersection of 

the epilayer surface and the misfit dislocation glide plane, and is a result of plastic shear

displacements (17). The two mechanisms are, in fact, not mutually exclusive. Therefore, along 

the path towards demonstration of a successful etched SiGe IR absorber layer, we report the 

results of a combined AFM and Nomarski microscope images of the SiGe layers with special 

focus on understanding crosshatching, because of the importance that crosshatching can play in 

producing high-performance devices. Next along that path, we employ optical reflectance and 

transmission to study the blackened Si1–xGex/Si materials.

Increased absorption of light is essential to create highly efficient photovoltaic devices. To 

achieve this, efficient 3-D structures with relevant material systems are required. Apart from 

these two techniques, others (18, 19) have proposed a technique in which multicrystalline SiGe 

bulk crystal with microscopic compositional distribution is grown using the casting technique. 

The average Ge composition was changed systematically between 0% and 10%. A small 

addition of Ge to multicrystalline Si was found to be very effective to increase the short-circuit 

current density without affecting the open-circuit voltage. They also indicated that such grown 

SiGe materials are promising candidates for solar cell and other optoelectronic applications. For 

such applications, SiGe has to be prepared with reduced reflectivity and increased absorbance. 

This can be achieved through surface texturing, as has been used in the case of black Si. In 

general, for a 3-D blackened surface, reactive ion etching or wet anisotropic etching are the 

techniques of choice. Although reactive ion etching can provide a structure with a high aspect 

ratio, it involves rather complicated procedures. MEE (20, 21), by which Si is etched using 

metal thin films or particle as catalysts, is an attractive procedure because it is simple and easier 

to perform with good results. 

2. Experiment 

The Si(x)Ge(1–x) alloy layers in this work were grown on 8-in Si substrates having either (111) or 

(100) orientation. The unusual growth method was accomplished using a special ultra-high 
4

vacuum (UHV)/chemical vapor deposition (CVD) reactor, which proceeds by decomposition of 

gas-phase Si (silane) and Ge (germane) compounds to deposit the Si(x)Ge(1–x) alloys of interest. 

Because there is a large lattice misfit between pure Si and the Si(x)Ge(1–x) alloy layers, a strategy 

to minimize lattice defects was that employs a graded lattice parameter that starts at a pure Si

buffer layer and ends at the alloy of interest. Three planar Si(x)Ge(1–x) alloys were prepared: 

Si60Ge40, Si70Ge30, and Si88Ge12. The substrates and all layers were intentionally doped n-type. 

The thickness of the layers differed slightly because the end-point alloy was different in each 

case. For the Si60Ge40 layer, the total thickness was 0.5 μm; for the Si70Ge30, the total thickness 

was 0.4 μm; and lastly for the Si88Ge12, the total thickness was 0.25 μm. 

Using such a large thickness assures that although some small residual strain probably exists 

after growth, the large misfit strain is mostly relaxed through the introduction of dislocations. 

However the graded lattice parameter approach minimizes that and yields device-quality 

material. In order to avoid strain-induced surface undulations in such highly compressively 

strained layers, the Si(x)Ge(1–x) alloy layers were grown at 350–400 °C. Although UHV-CVD 

growth allows highly perfect crystalline quality with little impurity incorporation even with 

growth rates as low as 10–3Å/s, the intentional doping was targeted to 2x1018/cm3donors, which

causes ionized impurity scattering of carriers. There was some variation in the measured Hall 

mobility, but the range was always <1000cm2/V-s because of alloy-scattering, and scattering 

from dislocations and ionized impurities.

Figure 2 gives the structure of the material grown with varying Ge concentration. Figure 2a is 

the depiction of the structure with growth of graded layers on an Si substrate with top layer of 

GeSi with varying Ge. The graded region thickness varies as one go from 12 % Ge in the first 

sample to the third sample 40%. 

(a)

(b) (c) (d)

Figure 2. (a) Structure of the grown material, (b) 12% GeSi on graded GeSi on the Si substrate, (c) 30% GeSi on 

graded GeSi on the Si substrate, and (d) 40% GeSi on graded GeSi on the Si substrate with all layers n+ 

doped. 

30% GeSi 2e18cm-3, 1000 nm

Graded GeSi 2e18cm-3

, 3000 nm

Si Substrate 1e18cm-3

12% GeSi 2e18cm-3, 1000 nm

Graded GeSi 2e18cm-3

, 1200 nm

Si Substrate 1e18cm-3

40% GeSi 2e18cm-3, 1000 nm

Graded GeSi 2e18cm-3

, 4000 nm

Si Substrate 1e18cm-3

Si Substrate 

Graded layers

 % GeSi 
5

The samples were inspected using AFM to make sure nanoparticles of gold (Au) are randomly 

oriented on the surface of Si1–xGex. In the next part of the experiment, a set of samples without 

Au were etched in solution of hydrogen fluoride (HF):hydrogen peroxide (H2O2):acetic acid 

(CH3COOH) (1:2:3). Care was taken to wait 30 min prior to using this etchant. The etching of 

the samples in the above solution showed linearity in the etch rate and proceeded to darkened 

surface. Once the etch rate was determined for different compositions of Si1–xGex, etching was 

carried out with a newly prepared solution of HF: H2O2: CH3COOH (1:2:3). After etching in that 

solution as part of the texturing process, the samples were thoroughly cleaned and blow dried 

with nitrogen. The solution etched Si1–xGex while slowly preserving the surface polish. 

However, etching the samples for more than 10 min showed visible damage. Finally, the etched 

samples were dipped in an aqueous solution of iodine (I) and potassium iodide (KI) (25 gm I and 

100 gm KI per liter of water [H2O]) (22). The samples were further cleaned in running deionized water and dried with nitrogen. These samples were further used for AFM surface 

analysis and optical reflection and transmission measurements using a Perkin Elmer 950 

ultraviolet (UV)-visible-near IR spectrometer. These steps are shown in figure 3.

Figure 3. Experimental procedure for the nano catalyst formation on the SiGe surface.

3. Results and Discussion

SiGe/Si samples with varying Ge were cleaned using standard procedures and surface of a 

number of samples were characterized using AFM and a Nomarski microscope. AFM is 

analogous to a surface profiler, where a sharp tip is dragged over the sample, and the movement 

of the tip is monitored as a measure of sample topography. Differential interference contrast 

microscopy (DIC), also known as Nomarski Interference Contrast (NIC) or the Nomarski 

microscopy, is an optical microscopy illumination technique used to enhance the contrast in 

unstained, transparent samples. DIC works on the principle of interferometry to gain 

information about the optical path length of the sample and see otherwise invisible features. A 

relatively complex lighting scheme produces an image with the object appearing black to white 

on a grey background. This image is similar to that obtained by phase contrast microscopy but 

Gold 

Nano Gold 

20 A gold deposition by 

e- beam evaporation

Anneal at 500 

C, 30min, and 

Ar Si <111>

Si1-xGex

Si <111>

Si1-xGex
6

without the bright diffraction halo. DIC works by separating a polarized light source into two 

orthogonally polarized mutually coherent parts which are spatially displaced (sheared) at the 

sample plane, and recombined before observation. The interference of the two parts at 

recombination is sensitive to their optical path difference (i.e., the product of refractive index and 

geometric path length). Adding an adjustable offset phase determining the interference at zero 

optical path difference in the sample, the contrast is proportional to the path length gradient 

along the shear direction, giving the appearance of a 3-D physical relief corresponding to the 

variation of optical density of the sample, emphasizing lines and edges though not providing a 

topographically accurate image. Figure 4 shows the Nomarski images of the surfaces of three 

samples.

(a) (b) (c) 

Figure 4. Nomarski images of the surfaces of three very thick p-type samples: (a) 15% Ge, (b) 30% Ge,

and (c) 50% Ge at 50×.

As shown in figure 4, sample (a) with 15% Ge clearly shows the crosshatch pattern. However, 

(b) and (c) indicate the 3-D island structuring. Despite the fact that the Si(x)Ge(1–x) alloys are very 

similar, the reason 3-D growth is observed in the layers of figure 4 and not in figure 5 is that a 

graded layer is used for the layers in figure 5, and the layers of figure 4 are grown without 

grading. Figure 5 depicts the Nomarski pictures of the three graded samples with (a) 12% Ge, 

(b) 30% Ge, and (c) 40% Ge in the SiGe/Si structure The crosshatch pattern is evident in all 

three better-grown samples and it appears that the pattern enlarges for higher concentration of 

Ge.
7

(a) (b) (c)

Figure 5. Normaski images of the surfaces of three n-type samples: (a) 12% Ge, (b) 30% Ge, and (c) 40% 

Ge at 50×.

The high concentration is evident in the AFM scan of the same samples, as shown in figure 6. 

The root mean square (rms) values were 1.22 nm, 3.29 nm, and 7.37 nm for samples (a), (b), and 

(c), respectively, indicating that the rms value doubles as one increases the concentration of Ge.

 

(a) (b) (c) 

Figure 6. AFM images of the surfaces of three samples: (a) 12% Ge, (b) 30% Ge, and (c) 40% Ge.

Figure 7 shows increasing step height and width of steps of the samples as the amount of Ge is 

increased from sample to sample, showing a peak-to-peak difference in the crosshatch as well as 

indirectly depicting the increase of the rms values as the amount of Ge increases. AFM clearly 

provides a good measure of the nature of the surface as the amount of Ge is increased from 

sample to sample. 

Some of the samples were thinned by lapping and polishing using a Logitech Lapping System. 

Here the goal was to make sure that the samples under consideration were double-side polished 

to reduce Rayleigh scattering during the pass-through of the IR light probe. Samples were 

cleaned and 20 Ǻ of Au was deposited on the Si1–xGex surface using an e-beam evaporator, 

which was kept at a pressure lower than 1x10–6 mTorr. Small pieces of these samples with 

appropriate masking were etched with HF:H2O2:CH3COOH (1:2:3). The etching solution was 

freshly prepared and left at room temperature for 30 min for stabilization before use. Etching 
8

was done at room temperature (25 °C) in polypropylene beakers with slight agitation. The 

samples were 1 cm2in area in area in ~100 ml of fresh solution of HF:H2O2:CH3COOH (1:2:3).

Figure 8 shows the etching depth with respect to time of Si1–xGex (with varying x values) in 

HF:H2O2:CH3COOH (1:2:3). 

(a) 

 

(b) 

(c) 

Figure 7. The step height from AFM images of the surfaces of three samples: (a) 12% Ge, (b) 30% Ge, and 

(c) 40% Ge.

Figure 8. Etch rate of Si1–xGex in HF:H2O2:CH3COOH (1:2:3).
9

The linear etching behavior is clearly evident from the Ge concentration in the Si1–xGex. The 

rapid increase in etch rate can be explained by the presence of an increased number of Ge surface 

atoms. The bonding energy reveals the difficulty in breaking the Si-Si bonds, which is 

78 kcal/mol; the Ge-Si bond dissociation energy is 72 kcal/mol and the Ge-Ge bond dissociation 

energy is 65 kcal/mol (23). The more Ge-Ge and Ge-Si bonds are exposed, the higher the 

etching rate is, as can be seen from the graph. The etched surface provided a greyish blackened 

surface. The etch rate was found to be less than 100 Å for Si0.85Ge0.15 , about 500 Å for 

Si0.70Ge0.30 and about 1300 for Si0.55 Ge0.45.

Optical measurements were performed as follows. After measuring the %T and %R, we used the 

equation, A = 1 – T – R, to obtain the absorbance. Unetched, etched, and thinned samples were 

used for the measurement of %T and %R, which we then applied to the above formula to 

calculate the percent absorbance. The results etched and unetched samples are plotted in figure 

9. The spectrum shows the reflectivity behavior of a thin film with a thickness of ~1.6 μm of the 

Si1–xGex layer on the Si (111) substrate. The spectrum shows considerable reduction in 

reflectivity for Si1-xGex samples after etching, as can be seen.

 

(a) (b) (c) 

Figure 9. %R of unetched and etched samples: (a) Si0.85Ge0.15, (b) Si0.70Ge0.30, and (c) Si0.50Ge0.50. 

As can be seen from the plots, the reflectivity goes through substantial reduction after the 

etching. The reflectivity reduces by ~85% for samples by MEE especially in the IR region. This 

lowering of reflectivity definitely indicates surface modification with micro-structure formation 

due to the wet etch processing. The etched samples were further characterized using a Veeco 

surface topography profiler. The system’s white light interferometry can measure surface 

topography from nanometer-scale roughness through millimeter-scale steps with sub-nanometer 

resolution. This surface metrology system was used to understand the surface texture patterns 

and parameters of the etched surface. Figure 10 gives the surface texture pattern of the sample 

Si0.70Ge0.30. The curves on the right indicate the x-axis (red) and y-axis (blue), as shown on the 

middle cross wire.
10

Figure 10. The surface texture pattern of the sample Si0.70Ge0.30.

4. Conclusion

We reported here, for the first time, an investigation of surface and optical properties of 

reflection and transmission of compositional Si1-xGex semiconductor alloys after treating them 

with metal enhanced chemical etching using nano-sized Au particles as the catalyst and 

HF:H2O2:CH3COOH as the etchant. The etched surface became black and textured, and showed 

a suppression of reflectivity and an enhancement of absorption in the near-IR region. 

Conceivably, the black Si1–xGex became micro-structured due to the metal catalysis and wet 

etching. Surface texturing was visible, as shown by the plots, and became extreme in the case of 

Si0.55Ge0.45. Visible separation in the x-y plots positively indicates this behavior, which is due to 

the lower amount of Si and an excess amount of Ge in Si1–xGex. Through this work, we have 

shown that Si1–xGex can be made black using metal enhanced chemical etching. We have also 

shown that such black Si1–xGex has reduced reflectivity and enhanced absorbance in the near-IR

region. 

Detectors made with this type of black Si1–xGex will have higher performance in the extended IR 

region. This lowering of reflection and enhancement of absorption may have important practical 

implications for making efficient photovoltaic and photodetecting applications using 

compositional Si1–xGex alloys. Currently, we are fabricating photodetectors to prove our 

conclusion.

 
11

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632.
13

List of Symbols, Abbreviations, and Acronyms 

2-D two-dimensional 

3-D three-dimensional 

AFM atomic force microscopy 

ARL U.S. Army Research Laboratory 

Au gold 

CH3COOH acetic acid 

CVD chemical vapor deposition 

DIC differential interference contrast 

GaP gallium phosphide 

Ge germanium 

H2O water 

H2O2 hydrogen peroxide 

HF hydrogen fluoride 

HJ heterojunction 

I iodine 

InGaAs indium gallium arsenide 

IR infrared 

KI potassium iodide 

MEE metal enhanced etching 

NIC Nomarski Interference Contrast 

RMS root mean square 

Si silicon 

SiGe silicon germanium 
14

TEM transmission electron microscopy 

UHV ultra-high vacuum 

UV ultraviolet 
15

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 (12 COPIES) 

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16

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 M WRABACK 

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 N BAMBHA 

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 ATTN RDRL SEE O 

 P PELLEGRINO 

 ATTN RDRL SEE P GILLESPIE 

 ATTN RDRL SEG N MARK 

 ATTN RDRL SER E 

 A DARWISH 

 ATTN RDRL SER E P SHAH 

 ATTN RDRL SER L 

 A WICKENDEN 

 ATTN RDRL SER L B NICHOLS 

 ATTN RDRL SER L E ZAKAR 

 ATTN RDRL SER L M DUBEY 

 ATTN RDRL SER L M ERVIN 

 ATTN RDRL SER L 

 S KILPATRICK 

 ATTN RDRL SER 

 P AMIRTHARAJ 

 ATTN RDRLL-SEE-I 

 K S RAMSEY 

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